Welcome.
An example of a platformer is HERE, and numerous other tutorials, including RPG, are just below your post in this very section.
I would say trying to understand a full game, with all the unique variables that may have been used, without first understanding the basics of the system, would be impossible, regardless of the fact that if someone had created a full game, they would be foolish to release the full source in case any unscrupulous persons just changed a few things and released it as their own work.
I am a great cynic at heart :)
Best to try the tutorials then ask loads of questions.