Visual Studio has its own ASP.NET Engine which is responsible for running your web application so you don't have any problems running an ASP.NET application from the VS IDE. When you want to host your site for others to access so deploy your web site on the Web Server, a web server is responsible for providing a response to requests that come from clients. When various anonymous users come in, many request also come in and the web server will give the response for each of them. IIS (Internet Information Server) is a group of Internet servers (including a Web or Hypertext Transfer Protocol server and a File Transfer Protocol server) with additional capabilities for Microsoft's Windows NT and Windows 2000 Server operating systems. IIS has its own ASP.NET Process to handle ASP.NET requests. If you look at this picture:
1. Client will send request to web browser.
2. The Web server will check request and pass the request to ASP.NET process.
3. The ASP.NET process engine will process the request and pass the response to the client using the web server.IIS handling the each and every request