Chances are, your electric guitar or bass has some knobs on it, usually named “Volume” and “Tone”. There are a few variations on how many of each of these you are likely to see on a “normal” guitar, but once you understand a single volume and a single tone control, you’ll understand any of the different setups available.
Underneath and attached to the knobs on your guitar are the devices that do the actual work, the potentiometers or “pots”. They will usually be three terminal devices and look something like the picture to the right
According to this useful link, you are probably familiar with the basics of what these things do to your sound. The volume control turns up or down the volume of the signal your guitar sends to the amplifier and the tone control makes the tone of the guitar duller, muddier, mellower or one of those adjectives people use to describe less treble.
Active electronics on a guitar or bass can have a few more functions, but let’s leave those alone for now and concentrate on what you are likely to see on 99.999% of the electric stringed instruments out there, the passive volume and tone controls.
While you are pretty sure about what these things do in general, do you know how they work?
The potentiometer type most commonly found in an electric guitar has a rotating shaft that you use to control two variable resistors at once. A resistor is a two terminal, passive electronic device that resists the flow of electricity. In a pot, the resistance changes depending on where the control shaft is turned.
Refer to the picture on the left: Think of the pot as a variable resistor between points A and W and a separate resistor between points B and W. As you turn the shaft one way, the resistance between A and W increases, while the resistance between B and W decreases. Turn the shaft the other way and you get the reverse; the resistance between B and W increases, while the resistance between A and W decreases.
For example, for the volume control on a typical guitar, the signal from the pickup(s) or the pickup selector would go to terminal A, terminal B would be tied to ground, and terminal W would go to the guitar’s output jack. You can think of it as the shaft deciding how much of terminal A vs how much of terminal B to send to the guitar cable from terminal W.