Three Point Lighting

Key Light: The key light is the main source of illumination on the character, it's placed traditionally at a 45 degree angle from where the camera is facing. It's set at this angle to add definition to the side of the face and shoulders. It can make the a lot of dark shadows on the face and make the scene look very 'gritty'. Which could be very good for an evil character in a horror film.

Fill Light:
This light fills in the shadows on the character that has been created by a key light. This is placed traditionally 45 degrees from the camera again, but on the opposite side. The fill light also has to be less intense than the key light so it doesn't compete with it, this can be done by moving the light further away or using a bulb with less voltage.  The fill light gives the character a much more even look, it softens the shadows not completely gets rid of them. This leaves a very natural even appearance.

Back Light:
This light is placed behind the character to make them stand out from the background and only spills onto the character. The light is placed above and out of the frame so it is not visible by the camera. The back light makes the audience focus their attention on the subject, which is good when the character is doing something important that the audience needs to see.  It causes the subject to have a slight glow and importance to the rest of the scene.