Potentiometer controls clock frequency.
How it works...
The operational amplifier detects that its legs (-,+) are different. Because the + leg is greater than the - leg, the op-amp outputs 5v. The + leg instantantly changes to a higher voltage while the - leg cannot due to the capacitor. The capacitor starts to charge as the current flows into it. Once the voltage on the + and - legs meet, the op-amp outputs 0v. The cap discharges until the volatge on the - leg is less than the + leg. The process then repeats until you flip the switch. The end.
I'm not explaining everything about an op-amp here. I know.
