http://guides.rubyonrails.org/getting_started.html
rails new -h
see all app builder switches
app/
Contains the controllers, models, views and assets for your application. You'll focus on this folder for the remainder of this guide.
config/
Configure your application's runtime rules, routes, database, and more. This is covered in more detail in Configuring Rails Applications
config.ru
Rack configuration for Rack based servers used to start the application.