1.You use commas to separate three or more things...for example: I like apples, oranges, and bananas.
2. To separate adjectives. She is a beautiful, smart woman.
3. use a comma before coordinating conjunction (and,but, for, or,etc.) Ex. I was going to to the library, but i changed my mind.
4. Use comma after introductory adverbs. (First, last, next)