Yeah... That sounds rather simple, but it's something everyone will have to do at some point in their life. Even people who will never sit in front of a sewing machine will want to sew a button back on a shirt at some point. So, everyone should know how to tie a knot in a piece of thread.
My daughter and I are taking sewing classes, and one of the things we learned early on was a quick and easy way to knot thread. (On purpose!) However, it was so easy, that I promptly forgot how to do it! Eek!
Well, Alicia is mending some of her doll's clothes and of course, we needed to knot a piece of thread. After a brief search on YouTube, I found what I needed. The sound on the video isn't very good, but you'll get the idea.