The three grommets in the bag are for mounting it on a wall, which is as simple as finding a nail or nails of the right length.  (Do yourself a favor and find something to cover the nail heads, like a substantial wad of duct tape, so you don't accidentally punch the face of nail.)

The zippered opening in the back of the bag allows you to remove or replace its contents.  Don't fill this bag with sand, though.  It is designed to be filled with larger material, such as dried beans, peas, or even shot.  I used mung bean acquired from a local Filipino store.

The single-section wall bag is available from the Immortal USA website.