Traditionally waist beads are worn along the hips semi-permanently, which means they are worn while bathing, sleeping, swimming, etc. until they break or they are cut off.
To tie them on, you simply place them around your waist, decide where you want them to sit, remove the excess beads and tie 3-4 knots. Once you are sure the beads are secure, cut off the excess string and beads.
Be sure not to tie them too tight or else they will break! Leave enough room for sitting, bending and bloating.