If you want to submit a patch to Chipmunk, it saves me a great deal of time and energy if you send me a pull request on GitHub. Sending a zip file of the modified source or a hand typed list of changes can be very tedious to integrate. A lot of times when given a patch of this form I won't have the time to look at it right away and I end up forgetting entirely. Given a proper patch file, I can apply the patch in a second or two and then easily browse the changes made to see what you changed.
Probably the best place to learn about Git is GitHub. They have a lot of walkthroughs that are better than anything I could write:https://github.com
Chipmunk's GitHub page:https://github.com/slembcke/Chipmunk-Physics