Now that the ASP.NET Worker Process has the request, it starts using .NET to process it (and here is where you can come in).

First, the request is passed to an HTTPRuntime object which is the start of the Pipeline (which is the above diagram). The HTTPRuntime examines the request and determines things like where it's going . It then creates an HTTPApplication object to process the request. The HTTPApplication essentially passes the request to a series of HTTPModule objects which simply examine and modify the request as necessary (Injection Point #1). Then the HTTPApplication object creates and passes the request (which is in an HTTPContext form) to the HTTPHandlers.

An HTTPHandler is anything that implements the IHTTPHandler interface. For example, the Page class implements IHTTPHandler and in your machine.config file, it says that all requests for .aspx files are passes to the PageHandlerFactory (which in time turns out your Page). This is Injection Point #2.