What controllers are and how to create them, and how ASP.NET invokes a controller via URLs ("routing").
This MSDN article explains what controllers and action methods are.
This excellent Pluralsight video explains controllers and routing.
Stephen Walther shows how the ASP.NET MVC framework maps browser requests to controller actions.
This MSDN article details routing in MVC 3
This MSDN article explains filters, which let you run code either before an action method is called or after an action method has run.
See "controllers" .