A ridgeline can be used for anything from a clothes line in your campsite, to hanging a tarp over a picnic table, tent, or hammock. A ridgeline is a very versatile tool to have in your arsenal for camping. This video refers to a knot called a Siberian Hitch, which is used to secure it to a tree.
For a complete guide to the basics of hammock camping, check out our Hammock Camping 101 article. After you have the ridgeline up, check out how to hang a tarp on it. And for more great how-to videos, go check out Black Owl on Youtube.