Functional Map of Installation

Newbie alert.
Is there a functional map of the WordPress files … i.e., a description of the files … maybe where to find where/how variables get assigned values, etc.
I managed to tweak the colors last night … my next thing is the Post heading text color … where is this defined/where to manipulate?
Is there a site reference or a good book that would just lay-out a typical site, MySQL – PHP-CSS driven, and show how the files interact and things work??
Thanks