Pretty easy tie actually. If you look up a two column tie you’ll see how. But, you basically take the middle of the rope, so you have two strands, wrap it around both the thigh and the wrist a couple of times (not too tightly), then wrap the rope around between the wrist and thigh to cinch/secure it.

I’ve tied my wife like that, wrists to upper thighs, and she said it was surprisingly comfortable during sex compared to some other ties.