When a photographer creates a photo there is an unwritten dialog between the author and the viewer. A topic is presented that will hopefully engages the viewer in a dialog. The dialog comes through the interplay of the viewer's eyes over the content of the image and is controlled by the photographer through the use of certain techniques (rule of thirds, leading lines, depth of field, contrast, and so on).
One technique I rely on to direct the viewer's eyes to my subject is through the manipulation of light. After all, we are using light to capture our scene, establish mood and shape our subject. This light can be manipulated in any number of ways: In a studio by placing the lights and adjusting ratios, or with natural light by using light shaping tools or the careful consideration of positions and backgrounds. There is also postprocessing manipulation of light in an image. All these techniques can be used to manipulate the light to where you want it.
As you come to study and understand light you will hear the term, "seeing the light," quite often. In truth, what this refers to is seeing the interplay of light and shadow and how it affects your subject. Color tone, saturation, contrast, edge transfer, specularity, are all qualities you will need to recognize but, for now, let's simplify things to three simple tones; white, middle gray and black. While this is a big oversimplification it will help make the process easy to understand.