1. Separate items in a list:
* I bought apples, oranges, and bananas at the store.
2. Set off introductory phrases or clauses:
* After the rain stopped, we went outside.
* To be honest, I'm not sure what to say.
3. Separate independent clauses joined by a coordinating conjunction:
* I went to the park, and I saw a dog playing.
4. Set off nonessential phrases or clauses:
* My friend, who lives in California, is coming to visit.
* The book, a novel by Jane Austen, was very interesting.
5. Separate direct address:
* John, please pass the salt.
6. Set off appositives (a word or phrase that renames or identifies another word or phrase):
* My dog, a golden retriever, loves to play fetch.
7. Set off parentheticals (words or phrases that are added to a sentence as an aside):
* The book, in my opinion, was excellent.
8. Separate city and state, day and month in dates:
* I live in Denver, Colorado.
* The party is on July 4th.
9. Separate contrasting elements:
* I like apples, but I don't like oranges.
These are just some of the most common uses of commas. There are many other situations where they can be used to clarify meaning and improve the flow of writing. It's important to learn the rules of comma usage so you can use them effectively in your own writing.