A potentiometer, short for pot, is a variable resistor. Turning the pot alters the electricity flow running through the resistance. This resistance is represented by a strip. As you move the shaft (the knob on the outside), youll modify the length electricity must cover to come out the other side of the pot. The more resistance strip itll cover, the more gain it will lose on its way out. When you come close to zero, the gain loss will be total giving you just silence.

Volume and Tone Pots

Is there a difference between volume and tone pots? The answer is no, volume and tone pots are essentially the same, although you might want to use different types of pots for volume and tone. The big difference is that tone pots have caps soldered on them to act as EQ. 

Split or Solid Shaft?

Split-shaft potentiometers usually work for plastic knobs. These are the best pots for Stratocasters. Solid-shaft pots work with metal knobs like the ones youll find in Fender Telecaster, for example. These knobs require a screw to stay in place.