When do people say "that's what I'm talking about?" I heard it quite a few times.

Rebecca

The phrase "that's what I'm talking about" expresses enthusiastic support for whatever "that" is in the context! It's similar to "that's excellent" or "that's great!" Ex: That's what I'm talking about! Our team deserved that win. Ex: A: Okay, you've convinced me. I'll come to the party. B: That's what I'm talking about! I'll see you later.