A web application starts when a browser requests a page of the application first time. The request is received by the IIS which then starts ASP.NET worker process (aspnet_wp.exe). The worker process then allocates a process space to the assembly and loads it. An application_start event occurs followed by Session_start. The request is then processed by the ASP.NET engine and sends back response in the form of HTML. The user receives the response in the form of page.
The page can be submitted to the server for further processing. The page submitting triggers postback event that causes the browser to send the page data, also called as view state to the server. When server receives view state, it creates new instance of the web form. The data is then restored from the view state to the control of the web form in Page_Init event.
The data in the control is then available in the Page_load event of the web form. The cached event is then handled and finally the event that caused the postback is processed. The web form is then destroyed. When the user stops using the application, Session_end event occurs and session ends. The default session time is 20 minutes. The application ends when no user accessing the application and this triggers Application_End event. Finally all the resources of the application are reclaimed by the Garbage collector.