IF I am looking at it correctly it looks like it is a removeable belt holster.
When you have a belt on you slide the holster thick tab (the part above the gun) upward between the pants and belt and then fold it back down over itself on the outside of the belt and basically folding the large tab in half over the belt. Then the thinner loop with the 'snap and dome' then goes around the thick tab that it has folded over and snaps closed below the belt....hopefully that makes sense. I have a SA holster like it, if my explanation isn't clear pm me and I can post a pic.