You have to move the king out of the way of a piece's attack on the other king, and the discovered attack must be checkmate.
For example:
The castle checkmate, which is (obviously) even harder, also counts.
I'd show you the game where I got it myself, but I can't find it. Plus, it's such a godawful game that it'd probably make some people on here want to puke.
i rreally wna thtis becuase my friend has it and wont let me hear the end of it.