This game requires a special controller that looks like a DJ turntable. The turntable has a record scratch and 7 keys arranged in a piano-key arrangement (4 white keys on the bottom, 3 black keys on the top, centered in front of the white keys).
Depending on the mode you choose to play, you have these lanes on-screen. Each lane is designated to a key on the turntable as well as the scratch. There is a marker that scrolls down the lane and as it reaches a line at the end, you must press the appropriate key. If you press the key with perfect timing, it will play a sound that's really a portion of the music. And if the note is for the scratch, you simply spin the turntable, which also produces a sound!
The sounds are a part of the soundtrack so if you're off by just a bit or completely miss it, the soundtrack will appear to be "incomplete" or "broken". If you keep hitting the notes with appropriate timing, you will hear a complete and whole soundtrack. Therefore, you'll have to know the song quite well to get a good score.
The game plays something like Dance Dance Revolution, but instead of just following the music, you get to make it.