The lighting in a video is one of the most important elements. Without the lighting the camera will not be able to function and will be useless to you. (Read about the relationships of lighting, camera, and the rest of the Video Family HERE)
When lighting a shot you have many different options to chose from. You could use the natural lighting or create your own lighting source using a variety of different methods.
One of the most basic method for lighting a subject and the base of more complex methods is Three Point Lighting. Three point lighting uses three different lights: Key Light- the main light set at a 45 degree angle from your subject. A Fill Light- set opposite side of the Key Light at 45 degrees to fill in and soften, but not remove, the shadows from the Key Light. And finally a Hair/Back Light- set behind the subject but out of the camera shot to separate the subject from the background.
Four point lighting is nearly identical to three point lighting. With the added fourth light that is positioned facing the background the subject is separated more from the background creating a greater depth of field.
By using different lighting techniques you can easily set the mood for your shot, whether dramatic or soft, lighting is the way to start. Click this link to learn more about setting the mood with lighting.
Here is an interesting video showing different ways to light with just one light.