You might want to start with procedures and conventions for contributing to the Evergreen project if you want to learn more about the process of becoming an Evergreen developer.
As we transition into an environment with a distributed set of code repositories, this page is an attempt to point to locations of code pertinent to Evergreen. You don't need to contribute to Evergreen if you're interested in our code - but it would be nice :)
These would normally be complete versions of the official core source code; either the base Git repositories, or up-to-date mirrors.