You would use commas in a list if the list contains three or more items. A comma would go between each item to separate them. In front of the last item, you should use the word "and" or "or". You can use a comma in front of "and" or "or" if wanted, but it isn't necessary.
Examples:
- She ate soup, a sandwich, and some chips for dinner.
- He went to the mall to buy a whole new outfit: some new shoes, a new shirt, new pants and even a new hat.
- Every night we play a board game. My mother, brother and two sisters always fight over what game piece they want to be.
- I'm deciding on what to eat for lunch; I will either eat at the McDonald's down the street, make some macaroni at home, or go to the Mexican restaurant with my friends.