how to set up custom error page for my asp.net app?

In my web.config file I see this tag and I moved the --> comment tag to where it is here (uncommented the customErrors tag
<authentication mode="Windows"/>
<!--
    The <customErrors> section enables configuration
    of what to do if/when an unhandled error occurs
    during the execution of a request. Specifically,
    it enables developers to configure html error pages
    to be displayed in place of a error stack trace.
-->
<customErrors mode="RemoteOnly" defaultRedirect="GenericErrorPage.htm">
    <error statusCode="403" redirect="NoAccess.htm" />
    <error statusCode="404" redirect="FileNotFound.htm" />
</customErrors> 
I created the 3 htm pages here and placed them in the active w ...