Use a period after a declarative or imperative statement: I went to the library. Sign your name here.
Use a question mark after a direct question or to indicate uncertainty: What is your name? Chaucer's dates are 1340?–1400. Do not use a question mark after an indirect question: I asked them what time they were leaving.
Use an exclamation point after an exclamatory or emphatic sentence or an interjection: Give me a break! Hey! Ouch! Wow!