Comment Start at main (Score 1) 329
I was in the same boat and ended up just looking around on sourceforge.net for a project that was interesting. Sort by your language, C++, and pick something in pre-alpha (code is usually smaller). From there, find the "int main" and start following the code, line by line; if you get lost, google it or e-mail the maintainers. Download a copy of the source and start tinkering, break it, and repeat.