Here is a great guide to getting your compiler up and running. It's a few megabytes so give it time to load if you have a slow connection.
I myself have only started tinkering with the camera code and controlling motors with it and whatnot. I'm pretty sure most of what you'll be using for the camera is in user_routines.c. From what I have found most of the stuff that communicates the camera with the rest of your robot is in here. Look for lines like this: "#if _USE_CMU_CAMERA" in the code to find sections relating to the camera.
Also, be sure
to download this guide. It has code explanation, a getting started guide, the GUI for calibrating the camera, and the 71-page user guide.