Use a comma to set off the words yes and no (e.g., Yes, thank you), to set off a tag question from the rest of the sentence (e.g., It's true, isn't it?), and to indicate direct address (e.g., Is that you, Steve?).

It's quite the substandard, isn't it? This little ray of sunshine asks students to further improve their understanding of punctuation. In particular, it focuses on the usage of commas when answering yes or no questions and directly addressing an audience.