[ioddly]

Check the documentation, if there is any. I've actually tried to add a small section on "where to start reading the code" to my larger projects. If it's a web application for example, you'd probably want to start where the routes are defined and go from there to whatever subsystem you're trying to modify or understand.

[kthejoker2]

And if there's no documentation, write some! Another great way to learn, rubber duck it in writing.