A comma is a hard working punctuation mark. It does many jobs for many purposes. Commas are used:
Between the name of a city and the state, province, or country, as in San Francisco, California.
My doctor, Dr. Lee, is very knowledgeable.
Bill put his notebook, textbooks, and lunch in his backpack.
To separate independent clauses when they are joined by the conjunctions and, but, or, nor, for, so, yet.
For example: The girls were sad, but they stayed strong.
The colorful, noisy birds were flying above us.
Don’t use a comma if the adjectives aren’t equal, as in
The light blue flowers were lovely.
Yes, I have met him before.
No, I don’t want that one.
Well, can I have another minute to decide?
David, have you meet Donna?