Grammar Study Guide: More Uses for Commas

We also use commas to set off introductory words at the beginnings of sentences and to set off the names of people who are being directly addressed.

Introductory Words: Words like yes, no, and well which are used to start a sentence are separated by a comma from the rest of the sentence.

Examples: Yes, you have to do your homework tonight.
"Well, let me think about that," said Mr. Walker

Direct Address: When you are speaking directly to someone, you set off what you are calling them, usually their name, by using a comma. This can happen at the beginning of a sentence, in the middle, or at the end.

Examples: Jessica, would you collect the homework please?
If I've told you once, young man, I've told you a thousand times to pick up your socks and put them in the laundry basket.
Isn't that right, Claudia? and I don't want any more, honey.

Both: You can also have an introductory word and a direct address in the same sentence. If that is the case, then set off both the introductory word and the name of the person being spoken to with commas.

Examples: No, you can't go to the movies tonight, Michael.
Yes, Minh, I expect you to take out the trash.