Q. how do you end something?
A. When your afghan is long enough, crochet to the end of the row. There will be a loop still on your hook. Carefully make the loop double its size, and slip your hook out. Lay your hook aside.
Measure down 2 or 3 inches (going toward your skein of yarn. With your scissors, cut the yarn string. Lay your scissors aside. Move your unused skein out of your way, too.
Carefully take your open end of yarn (this is still attached to your afghan) and slip it through the loop you made. Tighten the loop, and you're done! All you have to do now is use your crochet hook to slip this tail back and forth out of sight.
The second video shows how to do this. Let me know if you still have questions.