This is designed to hold large pooper-scooper or plastic grocery bags. You will put the bag through the inner ring, and wrap it around the ring, then insert bag and inner ring into the larger ring from the top. They should hold the bag firm between them.

From that point, clean up, and then push the inner ring from the bottom to disconnect it from the upper bag. If you unroll the bag from around the inner bag, you can then tie it off. This is designed so no poo will touch the plastic, and the bag should have ample clean room to tie off and dispose of.

I picked stuff up using a smaller bag as a glove, but a pooper scooper or shovel should work as well, just be careful to not get any on the outer ring.