The opening on the back is for 'hiding' the straps and side flaps. Loosen the buckle and shove it all in both the side openings on the back. You can then use the pack as a pouch in (for example) a backpack.
I got this bag a few weeks ago. It’s my 4th waist pack/cross body bag and it’s my favourite one. I wanted a pocket on the back of the bag which a lot of waist packs don’t have. The only thing missing on this bag is a hook to hang keys on. And them straps at the bottom are designed to hold a jacket/sweater I’m not sure what the 2 holes on the side of the back are, maybe hand warmers?
