Wrap the yarn around your cardboard or book:
Remove it from the cardboard or book:
And put your pair of needles into it
Twist it up
A lot! You'll know it's done when the twist has a tendency to kink on itself when you don't hold it tightly (as seen in the second picture below.)
Now fold it in half and pull on the twists a little; it should come into a skein form.
Transfer all the loops onto the same needle (be careful not to let it unwind as you do this)
Now open your keyring. You can hold it open as you load the loops on it, or you can wedge something in there like a button, as shown.
Slip all the loops from the needle onto the keyring.