Lion Brand Yarns and The Knitting Site offer free video tutorials for how to cast off. Casting off is the process of sealing the end of a finished knitting project.
The basic idea of casting off involves creating a knot so that each stitch seals itself off rather than creating a new loop on the knitting needles. To begin, knit two stitches, then pass the first stitch over the second stitch, pulling both stitches together and off the needle. Then continue this process with each stitch in the row before cutting the working yarn and pulling it into a knot.