Hex nuts are paired with screws. Normally. The purpose of the hexagonal shape is for the ease of removing the nut from the screw. There is a tool for that, also shaped hexagonal, or you can simply use a pair of flat nosed pliers to hold the nut still while you unscrew with a screwdriver.
Crafters have found other uses of the hex nuts, though. With some laces, ribbons or twine, the nuts are nice parts of bracelets, necklaces, earrings and anklets. Just search Google images and you will get lots of ideas. You are only limited by your imagination.