127.0.0.1 is what is known as a localhost address. It can ONLY be used to connect to yourself as in connecting a client and a server that is running on the same PC.
The command for a client to join a server is simple the IP and port like 192.168.1.6:4321. Note that this is a local network IP so the client needs to already be on the same LAN as the server to be able to connect.