Sentence: "Group of words that has a complete sense"
            e.g   I go to school.    We play a cricket.
These words as a group have a complete sense and called a sentence.

Now there are four types of  sentence.
1. Assertive sentence:  A sentence that make a assertion or statement is called Assertive or     Declarative sentence.
         e.g  Aslam sat on a wall.         Boys are making noise.
2. Interrogative sentence: A sentence that ask a question.
        e.g    Why are you playing here?         Who was making noise here?
3. Imperative sentence: A sentence that show a request or command.
       e.g     Shut the door.(Command)     Please forgive us.(Request) 
4. Exclamatory sentence: A sentence that show a strong and sudden feeling.
       e.g     Hurra! We have passed.    Alas! His father has dead.