asp.net How to redirect erros to a custom error page

Session state storage modes in ASP.NET

refer external config file in web.config

where is Machine.Config File?

ASP.NET : Display the number of visits on a page

All objects added to an IDictionary must have a Key attribute or some other type of key associated with them.- WPF

All erros redirected to ErrorPage.htm
except 404 errors are redirected to FileNotFound.aspx

<customErrors mode="On" defaultRedirect="ErrorPage.htm">
<error statusCode="404"
redirect="FileNotFound.aspx"/>
</customErrors>