I'm trying to figure out what the
Protected void Application_Start()
This is essentially the MVC frameworks bootstrap method to hook into the ASP.NET framework on startup. The
Application_Start gets called when the application domain is loaded. You can edit this file as you see fit and depending on what you chose when you created your now project some of these lines may or may not be included by default. What you have there.
AreaRegistration.RegisterAllAreas();- registers the areas, if you have an mvc application you can configure areas which are ways to further group functionality / views. See Areas for more detail.
WebApiConfig.Register(GlobalConfiguration.Configuration);- registers the Web API routing and additionally add global web api filters.
FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);- Add global mvc filters. See also previous SO question what this method does.
RouteConfig.RegisterRoutes(RouteTable.Routes);- initialize the mvc routing.