The Riffraff tool is an interactive toy that lets you trade licks with yourself. The On button is a toggle that turns it on and off. If you turn it on, you should hear a rhythm (assuming you have a General Midi synth, or at the very least assuming you have drum sounds on channel 10). If you play something on your MIDI keyboard, you will hear it echoed with about an 8 beat delay. However, it is not echoed verbatim - what you hear is a variation of what you played. The default rhythm has bass notes as well, so you will need to improvise in the key of G.

The More menu lets you alter the rhythms - there are two rhythms that are alternated, and you can set them independently. The rhythms have no bass notes, so you can improvise more freely if you change the rhythms.