We use comma after ‘Hi’, ‘Hello’, ‘Yes’, ‘No’, ‘Oh’, ‘Well’, etc.
Before ‘too’ at the end of a sentence.
Before or after a name.

Example:

Hello, Rita. Are you going to the class?

Yes, I am.

I go to the language club regularly.

Well, I don’t go there much.

I love your garden very much.

Oh, I love it, too!