Yes

Yes is the opposite of no. We usually use yes to show that we agree with something, accept something or are willing to do something:

A: Shall we stop for a coffee soon?
B: Yes. That’s a good idea.
A: Do you eat fish, Lisa?
B: Yes, absolutely.
A: Tim, can you work on the Rossiter Project with Will?
B: Yes. Sure.

We can use yes as a response token to show that we are listening to someone and that we agree, or simply that we want them to continue talking. In informal speaking, we often use yeah instead of yes, especially to show that we are listening:

A: I just added some garlic and chillies to the olive oil.
B: Yes.
A: Then I added just a little lemon juice.
B: Yeah. Right.
A: And some salt and pepper and that was it.
B: Really. It sounds so easy. I must try it sometime.

We use yes to answer negative questions and negative question tags:

A: Didn’t we visit Ellis Island when we went to New York?
B: Yes, we did.
A: Haven’t you got two sisters?
B: Yes. That’s right.
Not: ~~No, that’s right.~~
A: That’s Stuart over there, isn’t it?
B: Yes, it is. He’s got his brother with him too.