Where to get help about the Rails framework structure

Hi, I would like to understand better how Rails work... I mean how the framework is structured.

For instance, what happens when an address is requested for Apache or Webrick or any other? Which application is called first? How are plugins loaded? In which order? What happens before what? How validations are handled? Where goes a 'puts' output in a controller's action?

Are there any resources explaining how Rails is structure in this level of details? I could read the sources, but I would need to know where to start with. What is the main application in the framework. That one that loads environment.rb, routes.rb, plugins and so on...