As the name states, for this pose, you are balanced on the bottom bar of the hoop on the back of your waist. It can look somewhat similar to back balance, but the bar shouldn’t be in the same place. Since more of you body will be on one side of the hoop, you’ll probably need to steady yourself, for example with a foot on top of the hoop. Once you do that, you should be able to let go with your hands.
You can get in or out of this pose from seated, star on the bar, or hocks on the top, for instance.
You can see a simple demonstration at the Circus Dictionary.