1. To separate items in a list: This is the most common use of commas. You use a comma to separate each item in a list, except for the last item, which is usually followed by a conjunction like "and" or "or."
* Example: I bought apples, oranges, bananas, and grapes.
2. To separate independent clauses joined by a coordinating conjunction: When two complete sentences are joined by a coordinating conjunction (for, and, nor, but, or, yet, so), use a comma before the conjunction.
* Example: I went to the store, but it was closed.
3. To set off introductory phrases or clauses: Commas are used to separate introductory elements from the main part of the sentence.
* Example: After a long day, I was ready to relax.
4. To set off non-essential clauses or phrases: These are clauses or phrases that provide additional information but aren't necessary for the sentence's meaning. They are typically set off by commas on both sides.
* Example: The book, which was written by a famous author, was a bestseller.