How to pin the armature to a bone and move all the rest?

For example, I want to make an animation where the character is grabbled on a ledge and he’s hanging, or moving the legs, torso ecc. Since the central parts of the body usually lead the periferal ones, how to move it keeping the hand/s still in the same precise position?
I’m not going to create this, I just want to know “how” or what to search about.

As I said in your other post, watch the Humane Rigging tutorial. The question you’re asking here has no simple answer and once you dig into rigging with Nathan, you’ll see why it’s not a simple question and why there isn’t a simple answer.

Thanks anyway but I can’t buy anything because I’m moneyless. I’ll understand this in the future, then.

It has a Creative Commons 3 Attribution, so you can watch it here. You won’t have the rigs that come with it, but you’ll still get a lot out of it.