This image shows the basic 3 point lighting set up. By looking at the image alone you can kind of get a basic understanding of how and why these 3 lights are in the position they are, and what they are used for.
The key light, is what lights your subject, or the action happening in the scene, to not just make it visible but to also stand out a point of interest. This light, alongside the fill light, creates depth, and gives the audience a well lit, and clear shot of whatever is happening on screen. The back light makes the actor/point of action stand out from the background, to make it clear what should be visual to the audience first. It also in some way blocks out any shadows which may be unwanted.
The key & fill light are big lights which have an adjustable light control, which is beneficial as the person on lights, when on a gig, can increase or decrease the amount of light, to get a perfect image on camera in the different surroundings they may be in. Both of these are white light, where as the back light is a sort of orange light which cannot be dimmed. This can cause a bit of a problem, because if the lights are not positioned and set right, you could have a shot that looks too white, or too orange.
