Definition of three point lighting: the key light, fill light and rim light are used to achieve the three point lighting scheme
Here are steps to achieve this scheme:
1. You should first start in total darkness so when you add a light there should be no other lights interfering in the scene.
2. Add your key light! This is the subjects main illumination, which defines the most visable lighting and shadows. This is also the dominant lighting source, such as the sun, but can be positioned many different ways.

Create a spot light to serve as the Key. From the top view, offset the Key Light 15 to 45 degrees to the side (to the left or right) of the camera. From a side view, raise the Key Light above the camera, so that it hits your subject from about 15 to 45 degrees higher than the camera angle.
(http://www.3drender.com/light/3point.html)
key_light.jpg
3. Add your fill light(s), The Fill Light softens and extends the illumination provided by the key light, and makes more of the subject visible. Fill Light can simulate light from the sky (other than the sun), secondary light sources such as table lamps, or reflected and bounced light in your scene. With several functions for Fill Lights, you may add several of them to a scene. Spot lights are the most useful, but point lights may be used.
From the top view, a Fill Light should come from a generally opposite angle than the Key - if the Key is on the left, the Fill should be on the right - but don't make all of your lighting 100% symmetrical! The Fill can be raised to the subject's height, but should be lower than the Key.
3ptFill.jpg
4. Add Rim Light. The Rim Light (also called Back Light) creates a bright line around the edge of the object, to help visually separate the object from the background.
From the top view, add a spot light, and position it behind your subject, opposite from the camera. From the right view, position the Back Light above your subject.
3ptBackp.gif
For more information go to this youtube video:
http://www.youtube.com/watch?v=gkUqBJoxZ-I
By: Sydney Hall