Okay, so here's a quick demo of how I use the Tarp Key. As noted before, I use it on 1.75mm Zing It, and use a Klemheist knot which is like a Prusik Knot. It allows me to slide the key up and down the line.
Bloomgorge, has it set up where the line comes thru the hole at the bottom of the key. You would wrap it around the little notches and that would hold it in place. He also uses a different method to tie if off at the end. For me, I found the way I do it works for me. YMMV.
So, here it is. If you have any questions, as always feel free to ask.