Reverb occurs naturally when a sound is created in an enclosed space, and reflects from the walls. This effect can be created digitally, and is most noticeable when a sound cuts out suddenly and then continues to echo, slowly getting quieter.
The DJ software lets you repeat certain effects or parts of a song as much as you want. It started with CDJ players, where there was a “loop in” and “loop out” pair of buttons. You had to time precisely when you hit the buttons to get the perfect loop.