About web.config File
Web.config is the a settings and configuration file for IIS7+ web sites. It’s commonly used for ASP.NET web applications.
A web.config file is automatically created when your web hosting account is set up on one of our Ecenica Windows Shared-Hosting servers.
Web.config is the main settings and configuration file for an ASP.NET web application. The file is an XML document that defines configuration information regarding the web application. The web.config file contains information that control module loading, security configuration, session state configuration, and application language and compilation settings. Web.config files can also contain application specific items such as database connection strings. WikiPedia
For help restoring your web.config file see Web.config Default Settings.