Mountaineering knots can be divided into climbing knots, anchoring knots, joining knots and special knots. Every knot has its unique purpose and need to be applied at right place to be sure of safety and climbing without wasting energy (which can be saved by using right knots).
There is a universal knot which can be used for anchoring, climbing. Step by step guide to the knot is provided @http://www.scribd.com/doc/50119204/BowLine
Another used which is widely used for anchoring purpose is Figure of 8 (eight). Step by step guide is given @http://www.scribd.com/Figure-of-Eight/d/50119207
One need to be well aware of safety, this knot is used to complete variety of knots to make sure they do not open up.
In this case hold one hand fixed while move the running end on round of fixed end and pass thorough the loop as shown in the figure.
Note: End of the rope which can be moved freely is called moving end. Other hand of the rope where you have plenty of rope and which cannot be moved freely is called running end.