Study the right photo. That small piece of metal (4 x 2 inch) with a hole drilled in one end is the "handle". The Allen bolt goes into a nut, then through the "handle", then into the Rivet Nut.Place the Rivet Nut, handle and bolt assembly in the hole in the deck, hold onto the "handle" so it won't turn and tighten the nut (on the Allen bolt. Sometimes you'll need to also have to stop the Allen bolt from turning until the Rivet Nut starts to seat.)
The drawing below the photo is of a homemade installation tool. Hold the 'static' piece, to keep the rivet from rotating, and put about two turns on the rivet with the "nut" (that doesn't strip like a hex nut). A socket head allen bolt is the only high strength bolt I could find in this small size. A regular nut and bolt strips way too easily. Oh, better buy several of each for they wear out quickly.
Note: You can also buy a rivet gun with adapters to set the rivets. I honestly haven't tried it this way, but it's got to be an improvement.