Configuration settings and preferences of Mac OS X apps are usually stored in a so-called plist (Property List file) file, stored in the folder ~/Library/Preferences. These files store a list of properties in a serialized way, and are binary (not readable/editable).

Mac OS X itself has some tools to view and edit property lists but they are not very efficient and easy to use. Luckily, the internet provides all sort of (free) tools to perform the task of viewing/editing these files much more easily.

The most easy-to-use I found is Prefs Editor, written by Thomas Tempelmann.

It is a very easy to use, intuitive, and foremost, a free tool which can view and edit property lists in real-time. It's a true must-have if you want to do manual changes to configuration and settings of Apps, or even OS X itself.