Networking 103: How to use Custom Domains with a Reverse Proxy

A little networking 103 guide on how reverse proxies work to help you use custom domain names. This is not a tutorial, but just an overview of how it works. Hopefully it makes sense of other tutorials that can be more specific to your circumstance. With all the different domain registrars and routers out there, it's tough to create a tutorial for something like this.
Please be extra cautious if you decide to mess around with your firewall settings. Go out and research the security implications and make sure opening up ports is really what you need in your network. I would recommend sticking with a VPN if at all possible. I'm not a security expert but there are plenty of resources out there on how to keep your reverse proxy practices safe, and the security risks you are taking by doing so.