The direction of the light determines highlight and shadow. Only some are good for creating the clues we need.
Front Lighting: Comes from the direction of the camera. It fills the subject with highlight and provides little evidence of depth. Shadows fall behind. The camera sees no tonal variation or depth. This is flat lighting. Useful for portraits etc minimizing texture.
Back Lighting: Also fails to provide the clues. Shadow is thrown forward. The side facing the camera is in darkness. Suggests drama but without other lights there is no dimension.
Side Lighting: Provides both highlight and shadow and thus depth.
Top Lighting: Is a kind of side lighting. It provides the highlight and shadow we need to suggest depth.
All these divisions are degrees and they can vary around the subject. three-quarter lighting an example. All of these degrees can be justifiable depending on relationship and effects we wish to creat. Depth might not always be our aim. We need to think about light. It is not a fixed set of rules. These are just useful ideas. A simplification of the options available.
Shadows should be used with subtlety. They can overwhelm and distract.
We can use a combination of lights. We can fill and stop light with gobos and reflectors. Backgrounds and other objects in the area can creat reflections or deaden the light. The shape and form of the background and the supporting object add depth and structure to the images. A curved background and the position of light can creat fall off in the background revealing the nature of the elements of the image.