If you use the public instance you don’t need to set up or host or install anything. You can selfhost it if you want, but the public instance works just fine.
One person goes to the web page and starts a room. The other can join the same room by knowing the name of the room. (It will generate a link when you create a room to make it easy to send to someone so they can join by just clicking the link.)
They didn’t include https so the link doesn’t know what protocol it’s meant to open with
https://rye.astral.sh/