Grammar is a  science that deals with correct use of languageTranslate both in conversation and writing.

Sentence
     Group of words which makes complete sense.

Example :
The Earth goes around the sun.
Where do you come from ?

Phrase
      Group of words which makes sense but not complete sense.They have no subject or predicateof their own.

Example :
in search of.
as soon as possible.

Clause         
   Group of words which forms part of a sentence, and contains a subject and a predicate.

Example :
The man whom I hate.
While it is raining.

Types of Sentences

Statements or Assertion                 
     A sentence that makes a statement or assertion.

Example :
The sun rises in the east.
The cow eats grass.

Interrogative Sentence             
    A sentence that asks a question.

Example :
Why did you go there ?
How old are you ?


Imperative Sentence
     A sentence which expresses a command, a requestor or a wish.

Example :
Get out of the class.
sit down
.

Exclamatory Sentence
     A sentence which expresses a sudden, strong feeling.

Example :
How beautiful the sky is!
What a fine morning!