Guitar effects pedals, which are also called stomp boxes, are used by the musician to change the sound of their guitar. Stomp boxes get their name because of the "stomping" action needed to make the effect work. When the pedals are off, you are playing with the guitars clean (unaffected signal) sound coming out of your amp. When you step on it to turn it on, the signal that goes to the pedals are changed creating the desired effect.
