The electric bass was introduced in the 1950s as an alternative to the stand-up bass. As well as bringing portability to the bottom end, the bass guitar added new sounds to the bassist's palette and established a niche for itself in a wide range of popular music.
Volume Control
Most basses have a volume knob and a tone knob for each pickup; finding a bass with more than two pickups is rare. The volume knobs are easy to identify as turning them completely counterclockwise blocks all sound from the instrument. Usually bassists turn the volume knob fully clockwise and control volume at the amplifier.
Tone Control
The most common tone controls cut treble sounds. Turn the knob counterclockwise for less brightness. Beginning players tend to prefer middle settings to reduce finger noise.
Mixing Knob
Some instruments with two pickups have a knob that allows a blend of input from each pickup. Usually such a knob has a center position that allows equal amounts of input from both pickups. Turning the knob clockwise adds more of the bridge pickup, and a counterclockwise turn adds more of the neck pickup. A mixing knob is often paired with a master volume control.
Advanced Tone Controls
Some more expensive instruments will have two or three tone controls. These adjust bass and treble, or -- in the case of three knobs -- bass, midrange and treble.