I had trouble understanding how to do my knee exercises

Yesterday, I read something about exercises for my thigh muscle. This afternoon, I started having pain in the left thigh muscle. Earlier today, I was rereading some of the paperwork that I was sent home with after having left knee surgery yesterday. I looked at the papers on how to tighten my thigh muscles. I guess that I don't really have good thigh muscles. As much as I tried to send a signal from my brain to my thigh, the muscle would not tighten. I have no clue why I can't do this, but the paperwork says that this will help with pain. Oh well! Perhaps I'll try it again tomorrow! I'm frustrated!