The figure-of-eight on a bight is a very useful loop. It is generally tied in the end of the rope, and can be clipped into anything to secure the end of the rope.
It is often used to set up a single rope for abseiling, or to be the end of an individual's safety line (usually with a carabiner).
It is also used if a climber is tying into the niddle of a climbing rope, as the pull is still only in one direction.
You should be aware that this knot can unroll under relatively low forces if loaded sideways from both directions ie perpendicular to the loop direction, particularly if nothing has been clipped into the loop. In that situation, an alpine butterfly may be a better choice.
|Start with a bight (loop) of rope in your hand.|
|Pass the loop under itself|
|Then back over itself ...|
|and finally through the loop formed from the bottom.|
|Pull the knot tight and set. A good knot should look the same from both top and bottom ie be symmetrical.|