Getting the belt protector off can be tricky. Turn the back of the iSkin to you. Spin the belt attachment until you form a + (cross). This should allow you to see a little switch in the "south" part of the +. Flick the switch as far right as it goes to "unlock" the belt clip. At this point you can shift the ENTIRE clip mechanism straight down, allowing you to easily pop the "southern" part out of it's mounting. Spin the entire mechanism clockwise or counter-clockwise 90 degrees, and you'll be able to detach what was the northern leg of the +, once you hit the right angle. It sounds complicated, but is quite easy.
You insert the iPod THROUGH the screen hole. It'll stretch, then return to it's standard shape.
If it came with a screen guard, that fits in after the iPod is firmly in place.