If Hop has warned you about Router Issues, or your're simply unable to connect to your Hop server, you probably need to enable UPnP on your router. On some routers, you'll need to manually configure port forwarding.
This is the first thing to try. Web search is probably the best place to look for info on whether or not your router supports UPnP, and how to enable it. If UPnP is up and running, that should be all Hop needs.
If you can't enable UPnP, you will need to manually forward ports to your Mac.
The default Hop ports are: TCP 1194, UDP 1194, TCP 443, and TCP 993. You'll need to configure your router to forward these ports to the Mac running your Hop server. Router configuration interfaces vary greatly between different manufacturers, and it's likely that web searching will be the best way to learn how to configure your router.
After you've configured your router, the best way to test it is via the Hop Doctor in your Hop app. (See User Guide: Mac for more information)