What is the difference between "Web.Config" and "Machine.Config" ?

Answer:

"Web.Config" files apply changes to each web application.
"Machine.Config" files apply settings to all ASP.NET applications.

You can override settings in the Machine.Config file for all the applications in a particular Web site by placing a Web.Config file in the root directory of the Web site as follows:

\InetPub\wwwroot\Web.Config