Rule 1: When seperating phrases that don't need to be there.
ex: My cat, Evan, likes to explode randomly.
Rule 2: When linking two independent clauses with a conjunction.
Ex: I want to play minecraft with Evan, but first I have to do my homework.
Rule 3: When adressing someone in particular.
Ex: Let's eat, Bob.
Rule 4: When making a list
Ex: We need to buy dog food, cereal, and 10 bottles of coca-cola.
Rule 5: When you have more than 1 ajd modyfying a noun.
Ex: The funny, hilarious Bob.
Rule 6: After intoductory phrases or clauses.
Ex: Once i'm done with dinner, i will play 5 nights at Freddy's at 11:59 pm.
Rule 7: Dates
Ex: November 12, 2014.
Rule 8: The ending of a letter.
Ex: I'll be back home by 8:30. Sincerly, Dad.
Rule 9: Geographic locations.
Ex: Iceland, Canada
When to not use a comma:
Rule 1: When seperating two independent clauses without a conjunction.
Rule 2: After the conjunction.
Rule 3: And finally, when sepeating a dependent and independent clause with a conjunction.