Yeah, I guessed you were trying to learn PHP - which is why I've been trying to steer you away from one of the more exotic and strange bits of the system that few people do understand, and towards something else.
It's like trying to learn a language from reading the dictionary - it won't tell you what you need to know.
Finding the code in SMF is easy - it all starts from the top index.php and it figures out where to go from there depending on what the user requests.
What I'd say is, figure out what you want to customise, then we can talk you through all the logic that gets to that point - just not the caching subsystem
