I thought those were for stacking, not icing. I've never heard of anyone icing with them.
This is what the steps are in an ad from an old American Cake Decorating magazine. You lightly ice the sides of the ring and place it on top of a cake board that fits. Then you place a layer of cake and pipe icing around the side for the dam. Fill it with whatever, place your next layer of cake and repeat. On top of your last layer you fill it with icing and level it off. Chill it for however long and hit the sides with a blow torch. Last you slide the ring off and your cake is crumb coated.
Wow!!! Those are REALLy expensive. I think I'd check Fat Daddios prices before I invest in those - apparently they intend them to be family heirlooms. WOW!