I made this because my purple yarn was coming to an end and it no longer formed a ball, and it was getting all tangled. I have to idea what the cardboard is called, like, if it has a real name or what. So, I'm just going to call it the paper towel holder thingy. XD
(Sorry, I didn't take any pictures. But it's really simple!)
Okay, so take your paper towel or toilet paper cardboard holder, whichever you please and cut one diagnal slit in each side.
Put one end of your yarn in one slit, and then wrap the yarn around then take the end peice of the yarn and put it in the opposite slit.
(I told you it was simple.) :)