There are many definitions of the sentence and these definitions differ from each other because the scientists approach from different viewpoints to this question [12; 44].
“The sentence is the immediate integral unit of speech built up of words according to a definite syntactic pattern and distinguished by a contextually relevant communicative purpose”. A sentence is a unit of speech whose grammatical structure conforms to the laws of the language and which serves as the chief means of conveying a thought. A sentence is not only a means of communicating something about reality but also a means of showing the speaker’s attitude to it [12; 44].
The sentence is the base of the English language. We need to know how to build a strong base and what we can and cannot add to it. Grammar is the study of sentence structure and how words relate to one another in a sentence .
Each complete thought that we write is a sentence.
A sentence can be a statement: The sun sets in the evening.
A sentence can be a question: When do you go to work in the morning?
A sentence can be a command or an exclamation: Get out of my kitchen!
A sentence always starts with a capital letter and ends with some kind of punctuation mark (period, question mark, exclamation point, etc.) 
A simple sentence includes a single subject and verb group. E.g. Mary and John worked and studied together .
Simple sentences, both two-member and one-member, can be unextended and extended.
A simple sentence may be unextended if it consists only of the main parts of the sentence – the subject and the predicate. A sentence is extended if it includes some secondary parts (the attribute, the object, the adverbial modifier) .
She is a student.
An extended sentence is a sentence consisting of the subject, the predicate and one or more secondary parts (objects, attributes, or adverbial modifiers) [3; 269].
The two native women stole furtive glances at Sarie (Abrahams).
There are many approaches to classify sentences. Below we shall consider only some of them.
There are two principles of sentences classifying:
1) types of communication. Applying this principle there are 3 types of sentences: declarative, interrogative, imperative and exclamatory.
2) according to structure. Applying this principle there are two main types of sentences: simple and composite [12; 45].
From the point of view of the existence of all parts of the sentence we differentiate elliptical and non-elliptical sentences [12; 45].
According to their structure simple sentences are divided into two-member and one-member sentences [3; 267].
A two-member sentence has two members – a subject and a predicate [3; 267].
Fleur had established immediate contact with an architect (Galsworthy).
A two-member sentence may be complete or incomplete. It is complete when it has a subject and a predicate [3; 267].
Young Jolyon could not help smiling (Galsworthy).
It is incomplete when one of the principal parts or both of them are missing, but can be easily understood from the context. Such sentences are called elliptical and are mostly used in colloquial speech and especially in dialogue [3; 267].
Best not to see her again. Best to forget all about her (Abrahams).
What were you doing? Drinking (Shaw).
A one-member sentence is a sentence having only one member which is neither the subject nor the predicate [3; 267].
One-member sentences are generally used in descriptions and in emotional speech.
If the main part of a one-member sentence is expressed by a noun, the sentence is called nominal [3; 267].
Freedom! Bells ringing out, flowers, kisses, wine (Heym).
The main part of a one-member sentence is often expressed by an infinitive.
No! To have his friendship, his admiration, but not at that price (Galsworthy).
English sentence structure is the basic arrangement of a sentence. A sentence is made with a subject and a predicate, and maybe several other parts. The subject tells who or what the sentence is about. Then the verb and the rest of the predicate give information about what the subject does or is .
It is possible to have one word sentences in English: a verbal command like “Come!” or “Listen!” In commands, the unexpressed subject of the sentence is “you”. 
However, most English sentences begin with an actual subject (one or more nouns or pronouns, possibly with supporting adjectives) followed by a predicate (a verb or verbs and possibly modifiers, phrases, or objects.) 
Besides simple sentences, it is possible to have a compound subject or verb, a compound sentence (two subject-predicate clauses combined with a comma and conjunction or with a semicolon), or a complex sentence (two subject-predicate clauses combined in a way that makes one subordinate to the other) 
In questions the subject (S) follows the helping verb (HV) but precedes the main verb (MV) and the rest of the sentence, so the predicate is divided: HV- S- MV- rest of sentence .
Does Jeff study every night?
Do Bill and Jeff work together?
Can you swim?
Are they swimming right now?
Is Sarah going to the party?
A phrase is a group of words that gives information but is not a complete clause or sentence. (In other words, it does not include both a subject and a verb.) 
Prepositional Phrases are groups of words beginning with a preposition and including a noun or pronoun (with supporting adjectives, etc.):
Mary walked rapidly to the store
She wanted to get home before dark
I hope for an ‘A’ on the test tomorrow .
Predicates can also include direct or indirect objects. The subject does something to the direct object: The boy hit the ball. Mom bought gifts. Certain verbs can also have an indirect object: The boy gave me the ball. Mom bought us gifts. Indirect objects always precede (go before) direct objects .
Instead of using an indirect object, you could express the same idea with a prepositional phrase using ‘to’ or ‘for’ after the direct object: He gave the ball to me. Mom bought gifts for us .
Here are two examples:
University students study subjects in great depth. (“Subjects” is the direct object.)
Some teachers give students a lot of homework. (“Homework” is the direct object; “students” is the indirect object.) .