Assuming there is some form of bug list associated with it that is often my preferred way to learn a new code base. Try to fix a bug and you'll soon find yours

Assuming there is some form of bug list associated with it that is often my preferred way to learn a new code base. Try to fix a bug and you'll soon find yourself having to learn how the code involved works, and with a goal your focus will be better than just reading through the code flow.