Since this project is really just for practice (and may, frankly, have turned out pretty scary looking), it's not absolutely necessary to weave in the ends, but if you want to go through all the motions of a real knitting project, or you want to use this piece as a coaster, you'll want to weave in the ends.
Weaving in ends is essential for knitting projects because it hides those loose ends and keeps everything nice and finished so you can use the finished project.
You can do this either by threading the end on a yarn needle and weaving it into some of the stitches, or do the same thing with a crochet hook.
