The cast off is very easy and is done by knitting only two stitches at a time then dropping the back stitch over the front stitch. This creates a finished edge that looks like a braid and will match that cast on edge if you
There are many types cast on's and cast off's, some are super stretchy, some aren't. In this course I have taught you the simplest non-stretchy cast on and cast off which is best for blankets.
Here's what a basic blanket looks like.