Familiarity with the structure of the sentence helps us to understand correctly

Sentence is the most important grammatical structure in many languages. If we want to know the meaning of a paragraph, or paragraphs, we should know the meaning of each sentence. Sentence specifies the appropriate meaning and role for every lingual element. If we disorganize the system of one sentence, we will have some words with no complete meaning; some of these words may have different meanings and some of them may take different roles like a noun, a verb, an adjective or an adverb. Suppose! If we disorganize the whole sentences of a paragraph or all paragraphs, it will be impossible to know the meaning of one paragraph or paragraph because the most significant structure of the language (sentence) is disorganized. In conclusion, sentences are very important for many languages. Basically, each book is made from sentences. If we have no sentence, we have no paragraph or paragraphs; it means the sentence is everything in many languages.


Introduction
It is completely obvious that everyone wants to know the meaning of a text clearly and easily.This is what every reader begins to study a book, reading means to seeking for meaning.If we focus on the understanding of different readers, we will find that each reader has his/her own perception; sometimes even completely different.Basically, we may ask ourselves the reason/reasons, why the meaning of one text differs from one reader to another.
We likely answer that knowledge of the readers is not the same level; this is a right answer, but mostly have been seen which two or more readers at the same level of knowledge percept differently from one text.For example, you have taught one subject in the same class for the students who are at the same educational level, but during the assessment you will see different answers for the same question from the same subject.
It is possible to say that it depends on the students' intelligence, that is right; but mostly we see some students almost at the same level of intelligence answer completely different.One text is like a law book; and the reader is like a judge.While we are reading a text sentence by sentence, we are sentencing.In another word, we are saying our perception to ourselves; also, we are going to ahead for concluding.
It means our understanding and perception commences from sentence; if we know the sentence/sentences correctly, we will know the whole text meaning as well as we want.Therefore, our perception from one text is dependent to our perception from sentence and sentences.
Finally, we can say sentence is the most important unit in many languages; if we know the simplest grammatical part but the core one, our perception starts and go to complete understanding.So, sentence is everything/ all things in some languages like English, Arabic, Persian, Pashto, etc.

What the sentence is?
According to some grammar books, a sentence is a group of words which relate together grammatically; all these words convey one complete thought or idea for listeners/readers.Based on a definition which has been declared by Oxford dictionary, a sentence is "a set of words expressing a statement, a question or an order, usually containing a subject and a verb.In written English sentences begin with a capital letter and end with a full stop/period (.), a question mark (?), or an exclamation mark/exclamation point (!)." (Hornby, 2013, p. 217) As Yamin (1393, p.212) pointed out, each sentence has at least two main parts; in other words, subject and verb are the two main parts of the sentence.It means we have no sentence without the subject and verb, the simple sentence has one subject and one verb.(Torres-Gouzerh, 2016, p. 131)

Kinds of sentence according to its form
Sentence is divided according to its form into three kinds.

Simple sentence
As it has been mentioned before, each simple sentence has one subject and one verb; but it does not mean which the simple sentence is made just from two words (one word as its subject and another one as its verb) because each subject may have its own belongings and also each verb may need its belongings too.For example, "Hamid wrote a letter" is a simple sentence but it is more than two words; because the meaning of its verb is not complete without "a letter" whereas, its verb (write) is a transitive verb, and it needs to the object.
In sentence "Hamid cried" the meaning is complete and it does not need to another word else, because the verb in this sentence is intransitive verb, so its meaning is complete.In these two written sentences are many possibilities which they can be longer than they are now.
For example, Hamid, who is my classmate wrote a letter for me.Hamid who is my friendly classmate wrote a truly letter for me etc. so, the length and number of words is dependent to the writer or speaker, but its main words are just two words (subject and verb).(Hall, 2003, p. 109) Compound sentence Aarts (2001, p. 231) says, what the sentence components show, the smallest compound sentence is made from two independent clauses.The compound sentence components are joined by a coordinating conjunction or semicolon.Therefore, compound sentences are made from two or more independent clauses.So, it is inferred that a compound sentence has no dependent clause.For example, Hamid is a teacher.Salim is a carpenter.Both sentences are simple sentences but independent.This is grammatically correct when we join them in one sentence by writing a coordinating conjunction.Hamid is a teacher, and Salim is a carpenter.The last sentence is compound sentence which both sentences as the components of the whole one (compound sentence) worth the same.
It is also correct and possible to put a semicolon instead of a coordinating conjunction to make a compound sentence.For example, Kabul is the capital of Afghanistan.Afghanistan has 34 provinces.These two simple sentences can be joined by a semicolon and make a compound sentence like: Afghanistan has 34 provinces; Kabul is the capital of Afghanistan.(Noam Chomsky, 1957, p. 138) According to Radford (2009, p. 310) believe, the coordinating conjunction is what we use to join independent clauses together, in many languages including English are only seven coordinating conjunctions; they are all one-syllable words as appear as you see: For, And, Nor, But, Or, Yet, and So for remembering them easily you can make a mnemonic word (FANBOYS).
Based on the usage of these coordinating conjunctions, these are not the same; because the words and, but and or, are used more than others.The using of a comma is considered before the coordination conjunction; if the compound sentence is very short, putting of comma is optional.As in following, we start to explain the using of coordinating conjunctions and semicolon.

And
The conjunction and is the most common one.We can use 'and' in several ways.
1.And can be used to join two clauses which have equal value, it means the relationship between clauses is equality.For example: Kabul is in Afghanistan, and Tehran is in Iran. 2. And is used to show the order of the occurring time, when we use and it is inferred which the second clause happened after the first one.it means the relationship between clauses is sequence.For example: The rain was finished and the flood began.3. Also and is used to connect two independent clauses as the cause and effect (result); for instance, there was no rain this year, and the farmers harvest is not good.(Yule, 2020, p. 98)

But
The word conjunction but is used to introduce a clause that contrasts or stands on the opposite site with the preceding clause, for example: Ahmad studied hardly, but he could not pass the exam.

Or
The conjunction or comes between two independent clauses which every clause can be alternative for other.For example, you can go to class 101, or 102.(Newson, 2006, p. 100)

Nor
When we have two clauses which the first one is in negative case with words neither or never, the second clause can be joined with nor, and both clauses do not happen.For example, Asad never did his homework, nor did he help his mother.(Hall, 2003, p. 127)

For
For, almost has the same meaning of 'because', it is used to relate two independent clauses which the first clause acts as a claim, the second clause is its reason.For instance, Ahmad failed in final exam, for he was playing volleyball all time.

Yet
Yet, means like but.For example: I have been friend with you; in these many years, yet I am unfamiliar with you.(Radford, 2009, p. 274)

So
There is almost one synonym for word so, this word is therefore.So connects those two independent clauses which the first one acts as the reason for the second clause.For instance, Musa had a headache, so he took a day off.(Yule, 2020, p. 219) It is remarkable that in a compound sentence, it is possible to omit some removable words like subject and modal auxiliary from the second clause.(Be aware of, it is not possible with complex sentences) (Aarts, 2001, p. 236) For example, I can drink a cup of tea, or I can drink another thing.We can use this sentence in another way.I can drink a cup of tea or drink another thing.

Semicolon
Also, independent clauses can be connected with a semicolon (;) to make compound sentences.For example, I felt a little dizzy last night; last night I went to bed earlier than other nights.
Yesterday Hamid did his homework; Nasim went to sightseeing; Musa stayed in his bed for all day.

Joining Compound Sentences with Conjunctive Adverbs
Independent clauses can be joined by words and phrases which are called conjunctive adverbs like moreover, however, at least, etc.When conjunctive adverbs are used to join independent clauses, during the usage of conjunctive adverb it is absolutely significant to use a semicolon (;) before it and a comma (,) after.(Meshkattuddini, 1366, p. 211) For example, I am trying to meet my instructor; however, I could not see him.
Social networks keep me very busy; moreover, it is very significant to keep ourselves informed.
The accident was happened; in fact, I could not believe it easily.

Complex Sentence
According to Hornby (2013, p. 107) in Oxford Learner's Dictionary, complex sentence is defined as "containing one main part (main clause of a sentence) and one or more other parts (called affixes or subordinate clauses)".Also, we can say, the simplest form of a complex sentence is a dependent clause plus to an independent clause.Of course, the independent clause and dependent clause of a complex sentence is joined by one subordinating conjunction.(Hall, 2003, p. 107) A complex sentence is defined as "a sentence containing at least one main clause and one subordinate clause."The Macmillan Dictionary defines a complex sentence as "a sentence consisting of an independent clause and one or more subordinate clauses."(Hornby, 2013, p. 74) It is significant to mention when we form the complex sentence we need to focus on.
-A complex sentence has its own structure.It has at least one independent clause and one subordinate clause we have to follow this formula.(Saidi, 1392, p. 200) -We have no complex sentence without a subordinating conjunction.It means that you have to use a subordinating conjunction to link the independent clause with dependent one.If the subordinating conjunction comes between the two clauses, we need no comma before it.But when we use the subordinating conjunction at the beginning of a sentence to form a dependent clause, we need to use a comma after it.(Mashkur, 1346, p. 143) -Also we can form a complex sentence by using a relative pronoun that called relative clauses which are also subordinate clauses.It means, in addition of using subordinating conjunction to form a complex sentence, it is possible to form a complex sentence with a relative pronoun.It is important to remember which a dependent clause joined to a complex sentence by a relative pronoun is called a relative clause.The rule of comma usage is as the rule of subordinating conjunction.
The relative clauses are some extra information about the subject or object in the sentence.(Sultani, 1376, p. 98) See the following examples: 1. Subordinating Conjunction in the Beginning • After we eat our lunch, we go to sightseeing.

Subordinating Conjunction in the Middle
• I could not do my homework because I was sick.(Faqehi, 1349, p. 112) 3. Complex Sentences with a Relative Clause as the Dependent Clause I, who passed his master exam, am a lecturer in Dari language and literature department of Bamyan University.If we pay attention to the structure of the complex sentence in different contexts, we will find it is possible that an independent clause can come at the beginning of the sentence, in the middle of the sentence, or maybe at the end of the sentence.
It is important to remember which complex sentences do not adhere to any predetermined pattern because of the mentioned reason.(Shariat, 1372, p. 216) and(Farshidward, 1382, p. 178) 1.Since they helped out, I finished everything on time.2. As soon as the initial introduction is over, we will have the prayer song.
Based on what Radford (2009, p. 70) said, the complex sentences are formed by centrality of the independent clause, which called the "main clause," then joining dependent clauses to the text body in order to add complementary information which extends on the information and facts provided by the main clause (central clause) of the sentence.

Difference between complex and compound Sentences
As Hall (2003, p. 107) says, a compound sentence differs from a complicated sentence in that it has multiple independent clauses but none that are reliant on one another.Dependent clauses are found in complex sentences, though.If a sentence has both at least one independent clause and at least one dependent clause, it is said to be complicated.
The way to identify a complex sentence.
• The only punctuation you need to be concerned about when using the proper subordinating conjunction in a complex sentence is the commas.The clause that comes first in a sentence determines whether or not a comma should be used: • A comma should occur just before the independent clause if the dependent clause comes first in the sentence.
• There is no necessity for a comma to be included if the independent clause comes first.(Aarts, 2001, p. 218) Kinds of the sentence according to its meaning Four distinct sentence types may be found in the English language.Sentence diversity increases readability and adds interest to your work.
1. Declarative sentences: A declarative sentence is one that makes a claim, presents a fact, provides an explanation, or conveys information in English grammar.Declarative statements are another name for these kinds of sentences.The most typical sentence structure in English is a declarative one.Declarative sentences are written in the present tense and often conclude with a period.The topic often comes before the verb.(Aarts, 2001, p. 321) 2. Exclamatory sentences: A sentence that exudes a strong emotion is referred to as an exclamatory sentence, exclamation sentence, or exclamative clause.Exclamatory sentences in English grammar often conclude with an exclamation mark, sometimes known as an exclamation point.Although they are acceptable in informal contexts, exclamatory sentences should never be used in professional writing, especially academic writing.(Noam Chomsky, 1957, p. 235) 3. A statement that provides a direct order, request, invitation, warning, or instruction is known as an imperative sentence.Without a subject, imperative statements convey instructions to an inferred second person.In the line "Wash the dinner plates," for instance, the implied subject is given the order to wash the dishes.(Yule, 2020, p. 146) 4. Question-posing sentences: A question-posing sentence is an interrogative sentence.
An interrogative statement can be direct or indirect, start with or without pronouns, and include tag questions, alternative questions, or yes/no interrogatives.Interrogative pronouns are frequently used at the beginning and conclusion of interrogative statements.Question words, often known as "wh" words, include "who," "what," "when," "where," "why," "which," "whose," and "whom."Auxiliary verbs can also be used in questions, such as "Did she mean to sound so angry?"As an auxiliary verb (also known as an assisting verb) in this instance, "did" changes the statement "she meant to sound so angry" into a question.(Faqehi, 1349, p. 130)

Conclusion
Sentences are groups of words that relate together grammatically, conveying one complete thought or idea for listeners/readers.Each sentence has at least two main parts, meaning subject and verb.
Sentences are divided into three types: simple sentences, compound sentences, and complex sentences.Simple sentences have one subject and one verb, but they may have different meanings and require different words.For example, "Hamid wrote a letter" is a simple sentence, but it is more than two words, as the meaning of its verb is not complete without "a letter" and its verb (write) needs to the object.
In contrast, "Hamid cried" is a complete sentence, meaning it doesn't need another word, as the verb in this sentence is intransitive and its meaning is complete.Compound sentences are at least two independent clauses which have been connected by one of coordinating conjunctions, or one semicolon.Compound sentences have no dependent clause.
Coordinating conjunctions are used to join independent clauses together, with seven in many languages including English.These one-syllable words are called for, and, but, and or are used more than others.Coordinating conjunctions are preceded by a comma rarely the using of a comma is optional.
The conjunction and is the most common, used to join two clauses with equal value, meaning the relationship between clauses is equality.
A complex sentence is a sentence containing one main clause and one or more other parts, called affixes or subordinate clauses.The simplest form of a complex sentence is a dependent clause plus to an independent clause, which is joined by one subordinating conjunction.A complex sentence has its own structure, with at least one independent clause and one subordinate clause.
When using a subordinating conjunction at the beginning of a sentence to form a dependent clause, a comma is needed.
Complex sentences are formed by the centrality of the independent clause, the "main clause," and joining dependent clauses to the text body to add complementary information.Complex sentences do not adhere to any predetermined pattern, as they can come at the beginning, middle, or end of the sentence.Compound sentences differ from complex sentences in that they have multiple independent clauses but none that are reliant on one another.Dependent clauses are found in complex sentences, but they are not reliant on one another.In summary, complex sentences are formed by the centrality of the independent clause and the addition of dependent clauses to the text body.