is  a group of words that expresses a complete thought.  It begins with a capital letter and ends with a period.

We saw all the animals

Declarative sentence

makes a statement.  It begins with a capital letter and ends with a period.

We will ride on the bus.

Interrogative sentence

asks a question. It begins with a capital letter and ends with a question mark.

Is this your house?

Exclamatory sentence

shows sudden or strong feeling.  It begins with a capital letter and ends with a exclamation point.

How quickly you finished your work!

You are amazing!