Cofigure Airport Extreme over IP address

I have an iMac with an Airport Extreme router with a Drobo N connected. How can I configure a port to allow direct access via the web

Thanks for any help as I am not a techie…

If you’re going to do it you need to understand what you’re doing and the risks involved in opening up your network to access from the outside. Google “Network Address Translation” and “Port Forwarding”.