Can someone tell me how these work?

I'm interested in buying cute beachy coasters for the OOT baskets, but I want to just get cheap ones. I found these and think they might be cute but how do they work?
Flip flop coaster

is it just a flat coaster that you put the drink on? or is it the kind that the glass slips into it? It looks like it is flat though sine there are like 2 pairs together? Help!