The figure eight knot is by far the most common used knot in rock climbing. It is a great knot, not only because it is safe, but also because it is very easy to visually inspect it after it has been tied. There are a few variations of the figure eight knot and the most-used one is called the “follow through” figure eight knot. This is the one that climbers use to connect themselves to the rope.
Other variations of the figure eight knot are often used for anchoring or tying ropes together. See images below