The three lights used in a traditional 3-point lighting is front light, side light and back light. The side light is set up at a 45 degree angle from the camera. The front light is set up right in front of the model/object or from the camera position. Back light is set up at a 180 degree angle from the camera. It faces the background.
In this picture, it shows how the side light works. The side light is at a 45 degree angle and you can clearly see the triangle that is created by the side light under the left eye. The left side of my face is almost completely dark so it focuses on the right side.
