I was brought up to believe that “and” was never preceded by a comma. My daughter said it always is (she loves her commas). Seems we were both wrong.

Evidently, these are the rules –

You can list A, B, and C as in James, Thabo, and Rista had a party.

or

you can list A, B and C as in James, Thabo and Rista had a party.

The comma is optional

However, if the list is only of two items, there’s no comma

A, and B is wrong as in James, and Thabo exchanged business cards.

A and B is right as in James and Thabo exchanged business cards.

That’s how you deal with lists, but in a sentence, if the “and” joins two independent clauses, there’s a comma, but if they are not independent, there’s no comma. Here are some examples.

Thatho dropped the glass and it smashed.

Richard finished his speech, and John raised his glass.

Thatho threw the ball and Willem caught it.

The door opened, and Rachel switched on the light.

Interestingly, MSWord will sometimes highlight the comma as incorrect and at other times not, but it does not appear to follow these rules, so you’re pretty much on your own, but with the above roadmap to guide you.