1. When separating phrases that don't need to be there.
Ex: My brother, David, is starting his new soccer game.
2. When linking two independent clauses with a conjunction.
Ex: I'll like to go to the party, but my mom told me to go do homework.
3. When your addressing someone in particular.
Ex: Anna ,can we play volley ball with you?
4. When making a list.
Ex: Let's go get some school supplies, like some paper, pencils, erasers, and highlighters.
5. When you have more than one adjective modifying a noun.
Ex: The huge, enormous roller coaster.
6. After introductory phrases or clauses.
Ex: Once I finish doing a cartwheel, I'll do a split.
The "other three" :
Ex: November 12, 2014
8. Ending of a letter
Ex: Don't forget your lunch! Love, mom
9. Geographic locations
Ex: Cumming, GA
When to NOT use a comma:
1. When separating two independent clauses without a conjunction.
2. After the conjunction.
3. When separating a dependent and independent clause with a conjunction.