There are four kinds of sentences:
A declarative sentence tells about something.
It begins with a capital letter.
It ends with a period (.)
Examples:
My family went to the National Museum.
I discovered that old coins were bigger and heavier than the ones we have today.
An interrogative sentence asks about something.
It begins with a capital letter.
It ends with a question mark (?)
Examples:
What did you see there?
How did they look?
An imperative sentence asks or requests someone to do something.
It begins with a capital letter.
It ends with a period (.)
Examples:
Ask the officer in charge.
Please take me to the ball game.
An exclamatory sentence expresses a strong feeling or emotion.
It begins with a capital letter.
It ends with an exclamation point (!)
Examples:
It's wonderful to hear about that!
I'm leaving!