Use commas (1) in compound sentences, (2) after introductory material, and (3) when a sentence is interrupted by conjunctive adverbs or nonessential information.
Use commas with (4) coordinate adjectives:
Use commas (5) between items in a series. (See Oxford Comma video in separate post.)
Review this information on sentence structures. Be prepared to identify each type of structure in class tomorrow. Also, begin writing/identifying each type within your narrative.