I don't understand this game, what exactly am I supposed to be doing?
Use the arrow keys to select a song, then enter to start.
When the song starts, you press Z-key, X-key, ,-key and .-key to tap the notes when they reach the bottom line of the respective lanes.
Try to keep up, we know its a bit too hard at the moment, and you might not make it if you're not a really into rhythm-games like stepmania.