It's kinda hard to make a port forwarding tutorial because it's not something you do in the HM, you have to do that in your router, and every router is a bit different.
The most simple scenario is to log into your router config, locate the Port Forwarding section and enter a new rule forwarding incoming port 80 to port 80 at the IP of your HM and save.
Each router will have a different menu setup that you have to navigate to get to the port forwarding section, some internet services and/or routers will reserve and not allow you to use port 80, in which case you need to add another listening port to the HM and forward that port instead.
So give it a try and see if port 80 will work on your system, if not I will point you to the info you need to add another listening port to the HM.