Routing is a pattern matching system which identifies the incoming request and decides what to do with that request. So the usual process will be carried out by this mechanism is that it maps the URL to a particular method (action) on a particular controller. The actions gets executed and returns an instance of ActionResult which handles the logic for rendering the HTML content in user's browser.
At run time the routing engine matches the incoming request URL pattern against the URL patterns defined in the Route table and process that accordingly.
A typical MVC project defines a 'Global.asax' file, which contains a single method 'Application_Start' within which various calls are made to various configuration methods to set up the application's working state. One of these calls is to the 'RegisterRoutes' method of the 'RouteConfig' class found in the 'App_Start' folder of the project which is responsible for configuring the routes for the application.