The function of end punctuation is to indicate to the reader that an idea is complete and to point up the tone and flow of how the sentence should be read.

There are three basic ways to end a sentence:

Period (.)

A period is used when the sentence is informational.

Question mark (?)

Question marks are used when a question is asked.
Who, what, when, where, why, and how are all words that indicate a question.

Exclamation point (!)

Exclamation points are used to indicate excitement, urgency, or shouting.