Bowline

From WildernessWiki.org

Form a loop in the rope

Bring the working end up through the loop, and pass it around the standing length

Pass the working end back down through the loop

Pull tight

The Bowline is a fixed-loop knot. It is popular because it is extremely easy to learn, and can be tied one-handed. Use the bowline in any occasion where you need a very secure loop which will not slip nor jam. It is difficult to visually confirm that a bowline has been tied correctly. For this reason, the Figure-eight Loop may be preferred.

How to Tie