To start using it, first create a free ZeroTier One account and create a network to get the network-id needed for the add-on settings, then install the add-on, fill in the network-id and start it. Check log for succesful startup.
It should show up as connected device in the network settings. Authorise the connected device, and install the ZeroTier One client on the computer from which you want to connect to the home network. Create and enter an API token, and the network-id, also authorize the device in your ZeroTier One Admin portal.
NOTE: I had to restart my Windows instance before it showed the connected network stats in the ZeroTier One client.
You should now be able to ping the remote IP address and login to your Hass.io instance.