Is this a Summit harness? If so, you''ll take that green rope and wrap it around the tree and then feed the the end with the prusic knot through the loop and snug it to the tree. You'll use the prusic knot to hold the rope in place on the trunk. Now, those metal hooks on you harness strap, you'll hook those to the loose loop hanging off the middle of the prusic knot. Make sure your knot has six loops wrapped around the rope itself. It'll need to have those 6 to tighten up in case you fall. That knot it designed to only tighten when downward force is applied, such as a fall. I like the supplied green rope with my harness, it's easy to use while climbing up/down with my climber.