Examples:
color blue favourite is My. (makes no sense, therefore it is not a sentence)
My favourite color is blue. (makes complete sense, therefore it is a sentence)

There are four kinds of sentences:
1. Assertive or Declarative Sentence (a statement)
2. Imperative Sentence (a command)
3. Interrogative Sentence (a question)
4. Exclamatory Sentence (an exclamation)

1. An assertive sentence is a sentence that states a fact. Such sentences are simple statements. They state, assert or declare something.

Examples:
Jan is a student.
She lives in a big city.

2. An imperative sentence gives a command, makes a request, or express a wish.

Examples:
Go to your room. (an order)
Please lend me your book. (a request)
Have a good time at the picnic. (a wish)

3. An exclamatory sentence expresses sudden and strong feelings, such as surprise, wonder, pity, sympathy, happiness or gratitude.

Examples:
What a shame!
Wow, what a game!

4. An interrogative sentence asks a question.

Examples:
What is your name?
Where do you live?