You will need one user who is the Admin and will run the Local game, and all Users will connect to the Admin's network. Instructions for each user - Admin and User - are below.
- Download and run ZeroTier on your machine
- Sign in to the web client (my.zerotier.com/network)
- Ensure it's set to private so rando's don't join
- Share the Network ID with all your users, and when they join click the checkbox in the in the "Auth?" Column