Crimp beads are used to finish the ends of beading wire (tigertail) - you just thread the end of the wire through the crimp bead, then through the clasp or jumpring connector, and then back through the crimp bead. Finish crimp by flattening it with chain or flat nose pliers, or alternatively using crimping pliers which give a nice finish to crimp tubes.
Crimp bead covers are designed to cover crimp beads to look like a small bead and make pieces look more finished.