Click the flag to start. You have to set the tempo (speed) first. Lower numbers make it slower and higher numbers make it faster. Then choose the treble (the tune) and/or the bass to play.
The music is Frere Jacques which I learnt to play at school. If you input a number that is too small, the tempo will set to 20 bpm. If you input a number that is too big, the tempo will set to 500 bpm. If you don't input a number, the default is 20 bpm. The treble and bass parts aren't exactly in time for some reason.