Loop playback allows you to continually play a section of music over and over. It is purely a sequencer playback feature (there is no notational symbol). For notation based repeats, see Repeats.
Loop Playback is a great way to practice in the privacy of your own home. Lay down some changes, set the tempo really slow, setup a loop, and shed. Slowly increase the tempo (no need to stop the loop) or transpose to a different key (again, no need to stop the loop). Now go and impress your friends.
To Loop Playback (main tab "Playback")
To Stop Loop Playback