Bead cups, bead caps and bead cones can be used differently depending on their depth and width but all essentially can be used to cover the end of a bead.
Slim, shallow caps like FN091 when placed over the end of a bead add a metallic accent to the bead and can be used to great effect in designs, and we use these caps in several of our kits. Place the bead inside the curve to give a metallic edge, flip the bead cap up the other way to create a halo effect if you are making little angels.
Deeper bead caps are useful for hiding the ends of your work - eg if you are bringing together several threads, if they are tucked inside the bead cap it will help neaten the appearance of your finished work. These deeper bead caps can also work beautifully as a feature on their own - make some simple stamens with beads and headpins, attach inside a bead cap for quick and easy floral earrings.