It's called sampling or looping... There is a floor pedal that he steps on... which starts recording... then he plays whatever part he wants to play.. then hits stop.... Then the loop pedal repeats it in the background... The DigiTech JamMan is a good loop pedal in which you can doo tons of stuff. Some artists like Keller Williams use multiple instruments to loop.... he will play a drum line... loop it... then go over and pick up the bass and play a bass line and loop that over the drums... then play a rhythm track and loop that... and then sing and play lead over it. It's pretty cool to watch.