What is an imperative sentence?

An imperative sentence is a type of sentence that gives advice or instructions or that expresses a request or command. (Compare with sentences that make a statement, ask a question, or express an exclamation.)

An imperative sentence typically begins with the base form of a verb, as in Go now! The implied subject you is said to be "understood" (or elliptical) : (You) go now! (See You Understood.)