I started by drawing the picture on the eraser with the pencil. Then I took the paring knife and cut around the drawing, trying to cut deep into the eraser but also go as smoothly with the lines of the drawing as possible. Then I took the knife to the side of the eraser and began cutting toward the drawing, about a third way down the side. When I got to the picture I took the newly cut piece of eraser in my fingers and gently pulled at it until it ripped away, careful to make sure it didn't take any needed hunk of picture with it. After a bit of experimenting I got the hang of it and a new stamp was made!
I already own ink for stamps (i have a set of lower case letter stamps) so I took that out and pressed my Mickey Mouse head into it and then pressed it onto scrap paper as a test. It worked quite well, if I do say so myself! I excitedly started on the moustache and found it was a bit more tricky. I ended up redoing the design on the other side of the eraser because I had accidentally cut off one end of the moustache. The third eraser ended up being a simple heart.