Crimp covers are a useful, but not essential finding to have in your bead tray. They can used to cover crimps and elasticated knots, creating a neater finish and added bling to your final piece of jewellery. Like most findings, crimp covers come in a range of metal colours, shapes and sizes. 
How to use crimp covers
Step 1:
Hold the crimp cover over the crimp with a pair of flat or chain nosed pliers
Step 2:
Gently squeeze the opposite sides together, but not too far
Step 3:
Alternately, squash the top and bottom of the crimp cover on both sides along with the middle
Step 4:
The crimp cover is in place once it resembles a sphere and completely encases the crimp
 
I have added a video to YouTube showing how to use crimp covers: https://www.youtube.com/watch?v=7sfL_fOIWGI