Plug the thing into the C64's cartridge slot, then power up and it automatically loads its own sequencer software. IIRC, the clock jack is for a pulse-48 clock signal (48 clocks per bar) which was common for drum machines like the Linn LM-2 or Oberheim DMX. I think the other one is a "punch-in pedal...

The first thing to check is the potentiometer. The filter knobs get worked a lot, and it's an old machine, so it might just be sketchy contacts. Try cleaning all the pots with a GOOD electronic control cleaner spray (I recommend LPS2) and see if it makes a difference. You'll have to remove the knobs...