Question

"a pedal steel guitar uses foot pedals and knee levers. what do they do?"

Answer 1

A pedal steel guitar uses foot pedals and knee levers. It allows the player to change pitches with his feet and knees (apex).   A pedal (or foot pedal) is something you can use if you want to alter the sound coming from your guitar or add various sound effects.

Answer 2

 It allows the player to change pitches with his feet and knees (apex).