Joining an existing team with a large codebase already in place can be daunting. What's the best approach;
I'm working on what is currently an approx 20k line C++ app & library (Edit: small in the grand scheme of things!). In industry I imagine you'd get an introduction by an experienced programmer. However if this is not the case, what can you do to start adding value as quickly as possible?
--
Summary of answers:
this post is a partial duplicate of the-best-way-to-familiarize-yourself-with-an-inherited-codebase
Start with some small task if possible, debug the code around your problem. Stepping through code in debug mode is the easiest way to learn how something works.