What is ASP.NET?
It extends the .NET platform with tools and libraries specifically for building web apps. ASP.NET extends .NET with web specific features such as templating to help with building dynamic web pages, Authentication to help users to authenticate using there social profiles and libraries for common web patterns.
What is the web api lifecycle of a message?
The client generates a request which is passed through the pipeline as a HttpRequestMessage. The HttpRequestMessage reaches the Routing dispatcher where the dispatches checks if the Route Handler.
The dispatcher loops through the available handlers and picks the one matching the request. If the routing handler passes the request on to the next stage, the request enters the Controller. The Action Invoker invokes the Controller Action using the binding and model state in the HttpActionContext.
The Controller action executes the code in the Action method and prepares the HttpResponseMessage.