Another way of making a slip knot is as follows:
Holding the tail of the wool and the nose end of the hook in your left hand. Using your right hand wrap the ball end of wool around the hook anti-clockwise and over the tail end.
With the hook in the centre of the loop you have created. Hook the ball end of the wool onto the hook and pull it under the tail end and up through the hole you have created. This is like tying a knot.
The thread you have pulled through the hole will now create a loop which will sit on your hook.