Photography requires an understanding of some fundamental concepts like exposure, aperture, shutter speed, depth of field, and so on. As one experiences these in the field the abstract concepts make more sense and become second nature in the practice of photography. I have stumbled on a very interesting Web site that offers visual explanations of many photographic concepts. Some topics and their visual or verbal explanations may be too esoteric and complex, but several applets allow the visitor to play around with the settings of aperture, shutter speed, ISO setting, and a few more and see the results right away. My recommendations are, Variables that Affect Exposure, Depth of Field, and Gamut Mapping. Try any others if you like, but these three will make understanding, and then explaining to others, some of the fundamentals of photographic variables.