photo=light, graph=write, therefore photography literally means "light writing."
that being said, a camera is just a box that captures and controls light. the three elements needed for photography are light (exposure), photo emulsion material (light reactive film or paper), and a light proof container to put it in (camera).
KEY DEFINITION: EXPOSURE means TO SHOW TO LIGHT
the camera additionally incorporates two controls to allow or limit exposure:
1. APERTURE - the opening that allows light in
2. SHUTTER - the device that controls how long we let light enter the opening
here's a great web page explaining the camera obscura a simple concept that was the beginning of modern photography.
also check out this video for a demonstration of how to make a pinhole camera out of an oatmeal box. we'll be watching it in class but wanted to post it here as a reference.
here's another good written resource on making an oatmeal box camera.