Cameras, whether the newest digital wonder or the (becoming old quickly) film cameras, share a lot of basic ideas and functions. If you know one, you can find the same functions in the other. Understanding how your camera works is the first step toward controlling it to get the pictures you want. For the sake of simplicity, I’ll talk about film cameras. The concepts are the same in digital cameras, it’s just the way digital cameras achieve each of the elements of exposure that vary.
Cameras are all just light-tight boxes that control the amount of light that falls onto a piece of film or digital sensor. They’re nothing magical, just a box. This controlled amount of light is called the “exposure.”