Photography is all about light. Without light, no matter how dim, you wouldn’t be able to make a photograph. However, that doesn’t mean that that’s all there is to photography.
The simplest of light's qualities is its direction relative to your camera. There are essentially three directions: frontal, side and backlighting. The three directions have a different effect on how three-dimensional your subject appears to be due to the that shadows are cast.
Frontal Lighting:
Is lighting that emanates either from brhind the camera of from the camera itself. Built-in or on-camera flash is a frontal light. Frontal lighting has one big advantage. It evenly illuminates your subject so metering is fairly straightforward. However, it tends to flatten a subject. The shadows cast by frontal light are behind the subject, out of sight from the camera's point of view. Shadows help to give a sense of shape and form to a subject. WIthout shadows a subject's shape becomes more ambiguous. Shadows can also add drama to a photo. Frontal light lacks drama, making a photo look more like a record shot and be less interesting for this reason.
Side Lighting:
Is light that falls on a subject at roughly ninety degrees to the camera. This means that one side of a subject will be lit and the other side will be in shadow. In terms of helping to convey a subject's shape and form this is ideal. Of the three directions, side lighting creates the strongest sense that a subject has three dimensions. There's always a catch however. The catch in this instance is contrast. side lighting doesn't evenly illuminate your subject.
From side lighting to frontal and back lighting. Figuring out that side lighting consists a ninety degree angle. Where a back lighting creates the result of a silhouette. But front lighting can make an image flat, unless you create a bit of side lighting to give depth.