Belt replacement. hi...well the belt is fine, its just that i can't figure out how its supposed to

Question

hi...well the belt is fine, its just that i can't figure out how its supposed to catch on to the hook thats connected to the handle that has the green and red arrows that say "belt on" and "belt off." the belt is just loose around the brush roll. the vacuum still works, it just doesn't seem right to have the belt on there if it's not "on" anything. how do i use the "belt on, belt off" handle to catch the belt so that it is actually "on" or "off" something?