What is a Sentence?

What this word Syntax literally means in Greek is, you know putting together and arranging, Sentence is a grammatically complete idea, or it's a bunch of words that say one complete thing. So all sentence have noun or pronoun Component ( Subject) and something that it is doing which is called predicate (The verb part) and sometimes that subject can sort of be implied 

Example:
The great big dog licked my face.
Subject= (The Grat big dog) 
predicate= (licked my face)

pick up that apple

where I am telling you to do something (order) that does not always have to be a subject said out loud. This sentence has an invisible, secret subject ( You)

Three Types of sentences

1. Declarative Sentence (Statement)

it is a sentence that just states a fact or an opinion, but it just makes a statement. 
it is a beautiful day
li hated baseball

2. Interrogative (Questions)

It is a question. so it asks a question
   Where did you go last night?

3. Imperative (order)

It is a command so when you tell someone to do something and it has no subject.

 Follow that dog

4-Exclamations (An expression of strong emotions)

It is a type of sentence or maybe a word that like an expression of really strong emotions or high volume for example ow!.lookout!