First, here are the things you'll need. Scissors and an old tube sock. It doesn't have to be pretty, unless you want it to be. Arts and crafts are up to you.
Step 1: Line up the cut
Next, cut the tube sock about two lengths down from the top. A good way to do this is to simply put your ipod or other device at the top of the sock and flip it over it's end. Or just slide it down. Whatever.