Hi Sanjeev,

Web.Config:Web.Config is Nothing but set the all setting for the Web Applications in asp.net.
One project can have more than one Web.Config files are created in asp.net.
Examples:Suppose you can created the connection string for the our project in Web Applications ,once you can created the connection string tha can be Access any whre with in the Project files.
<Appsettingd>
<web.config>
onnection string Name="";
</web.config>
</Appsettingd>
Machine.Config:Machine.Config is nothing bu the Set the Machine leve setting for the Project in Web Application.
Machine.Config is created for only one for the each project in Web Application

Web.Config

Web .config file is created when you create your new  ASP web project.

for each project you have a different web.config file.

web.config is application level.

Machine.Config

This file is created during the installation of .Net.

You have only one machine.config per server.

It is not application specific.