Rappy Bird is pretty much the same as Flappy Bird, except you're simultaneously trying to make a hip hop beat.
Use the keyboard keys E to I and D to J to make the bird jump and play different drum sounds.
Open up a rap acapella at the same time to give you something to jam along with.
If you're having to use far too many or too few drum hits just to stay alive, the slider at the bottom adjusts the gravity.
The "Download last beat" button is kind of bodged and probably won't work first time, but should be OK afterwards.