How exactly do skins work?

How exactly does it know where each part goes. When you view the skin it's seperated (like the head is over there and its ear is over there and it only has half a body or a whole body if its not identical on each side.) So how exactly does it know where each part goes or what style?

That's frankly what I'd love to know...I've yet to see any tutorial cover that...

When the model is made after a skin is needed... so they do this Wrap thing where I dunno exaclty how it works but its like a tyle and for that model it knows where bits of the tyle go and stuff... kinda strange you gotta ask sumone who has done it b4...

You make the model then, you unwrap it any way you want. You take the model and you flaten it so you can see every polygon on the model you can unwrap any way you want.