In Direct Address

Use commas to separate a noun of direct address (the person being spoken to) from the rest of the sentence.

Please, Carla, learn some new jokes.

Between Two Independent Clauses

Use a comma between two independent clauses that are joined by a coordinating conjunction (and, but, or, nor, for, so, or yet).

Aquarium workers love animals, so they regularly rescue injured ones.

The team rehabilitated the injured sea lion pups, and then they released them.