A three point lighting setup creates dimensions in your image by using light and shadow to highlight your subject and make them stand out from the background. A good lighting setup gives a three-dimensional appearance to a two-dimensional image.
This is the primary and brightest light cast on your subject. The key light is typically placed at the side of the camera at a 45 degree angle. You can achieve a variety of lighting styles by experimenting with the key light in different locations, angles, and heights.
This is typically 50-75% less bright than the key light. The fill light is typically placed on the opposite side of the camera from the key light and is used to fill in the shadow created by the key light on your subject. You can adjust how much light it throws by moving the distance of the light further or closer to your subject. The fill light should not create a second shadow from your subject. If you see a second shadow, the fill light is too bright and needs to be adjusted.
This is used to add definition and highlight the outline of your subject, creating a three-dimensional appearance within the two-dimensional surface of the image. The back light separates your subject from its background. It is typically placed behind and above your subject at a 45 degree angle.