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...

Thanks,

Rodrigo.