I've programmed with C for about 7 years now (10+ year linux user as well) and would like to help out with the community. I like the whole idea of "open source" and now I think its time that i put my skills to use in the programming world.

My question is:

On these big open source projects (30,000 line projects) whats the best way to jump into the code? These projects can be very difficult and complex to understand so whats the best way to jump right in? Is there a neutral program out there that can just step through code line by line like a debugger does?

How do you guys do it? I've been looking for books for a couple years now but had no luck on this topic. What do you guys think?

Do you guys use any tools to help you read code better? Let me know your strategies.