I figure we should start from the beginning - how exactly does a camera work? I realize this is a ho-hum topic for a lesson, but I find that like many other things I've done/learned, you need to know the basics. For example, most dancers would agree that ballet is the foundation for any good dance technique, but when when I younger I thought ballet was boring and I decided not to take it. I regret that decision - I especially wished I had ballet training when I was auditioning in college for dance productions and I simply could not compete with the dancers that had exquisite ballet technique.
So enough of the explanations, let's get some answers. I researched a bunch of websites for the most coherent answer, and I liked this one:
"Let’s say you spot your dolphin and lift your camera to your eye. What happens?
First, light bouncing off the dolphin passes into the camera, through a set of lenses, and onto a mirror. From there, the light bounces up and into a funny-shaped piece of glass called a pentaprism (penta means five, and the pentaprism has, you guessed it, five sides). Once light enters the pentaprism, it bounces around in a complicated way until it passes through the eyepiece and enters your eye.
The dolphin is swimming just below the water, but you have a feeling it’s about to surface. Wait for it, wait for it…there! You snap the picture. When you press the button on the camera, the mirror flips up out of the way. Instead of bouncing into the pentaprism, light from the dolphin passes directly to the back of the camera. There, it either hits photographic film and starts a chemical reaction, or else it impacts an array of light-sensitive cells that release a tiny electric charge in each activated cell. Either way, even though the dolphin’s long gone, you’ve captured its image. Congratulations!"
Here's another diagram explaining how the light enters the camera before the shot (i.e. while searching for the dolphin) and during the shot (i.e. taking the picture of the dolphin).
Lessons for another time would be how to control how much light gets into the camera - or more specifically, lenses, aperture, and shutter speed. But for now I thought just understanding how a camera works is a good starting point.