[hnarayanan]

First off, do not give up. This is a struggle for even the most experienced people when dealing with a sufficiently complex new system.

Try to focus on small, noticeable wins. Focus on a narrow part of the system that seems relevant, and try to start fiddling with and see what happens. If the system has tests, try going through them as it is often easier to understand how a system ought to behave than the details.