Many of JRiver's Media Network features require use of an Access Key. This is a six character string that is associated with the server (MC). You will find it on your server in Tools > Options > Media Network. You then enter it on your client program. This might be JRemote, Gizmo, or Media Center.
This key is automatically registered with JRiver's servers. It is associated with two IP addresses. One is for your server, as seen from inside your network (local), and the other is your outside address (Internet). The Access Key method will work even if your outside address changes from time to time. To achieve access from outside your network, your router must forward requests to the correct PC, and your firewall must allow access on the port being used. Please see the topic called "Network Access" for more information.
IP Address Method
If you prefer, you can use an IP address to connect. In most cases, when you are asked for the Access Key, you can instead enter an IP address.
JRiver's Interact forum has a board on Remotes and on Media Network.