The direction of light will determine where shadows will be. By looking at the shadows in a picture, you can determine where the light comes from. This direction, more than any other light feature will affect the LOOK of a picture. Directions of light are given from the subjects point of view, thus back light points into the camera lens. There are no rules about which direction to use, the main reason for study of them is to control their effect on our subject.
Front light is used to show detail.
Few good outdoor shots use this type of light because it eliminates texture. This type of light is what comes out of a flash attachment and evenly lights our subject. It is the worst of the hard light types and would be better as soft light if a choice is possible. Side light emphasizes texture and shape. A strong side light from a window or a sunset causes long shadows and a dark side and light side relationship on a subject.