There are many ways to use commas in your writing. Below are some important ways that you should be familiar with while writing:
1. To separate adjectives.
I like to wear old, moldy socks when I play basketball.
2. To set off dialogue.
Oscar the Grouch said, "One man's trash is another
man's treasure."
"One man's trash is another man's treasure," said
Oscar the Grouch.
(notice the comma placement)
3. To set off interjections.
Wow, you really did it this time!
4. In a direct address.
Carla, watch out!
(notice -no quotes)
5. To set off appositives.
My father, a great cook, makes the best pizza in town.
(an appositive is a word or phrase that renames the noun or
pronoun before it)
6. Between two independent clauses.
I always bring a lot of work home, and I expect to get
good grades.
(An independent clause can stand alone as its own sentence.
If you combine two sentences then use a comma before the conjunction
[and, but, or, so, yet, etc...])
7. A series (3 or more words used in a row)
I love to eat ice cream, cake, candy, and pie!