So looking at it it's 2 parts that get locked together. A ring part that you place the shaft and balls through. Then the container that when placed over the shaft and locked to the ring leaves a gap the balls can no longer get through. Thus it is attached until the lock is released and the ring and container are separated again.
It's a chastity device so the point is that when it's on you can't actually do anything sexual with the contained bits (or maybe it's painful if aroused and some get off on that). The secondary sexual goals are any emotional arousal from fear/trust/control/submission/etc.
