The computer must be on campus or connected to a campus network with a VPN.
Step-by-step guide
Plug the Ethernet Cable into the port in the wall (Dorm rooms should have two Ethernet ports, one on each side of the room).
Plug the other end of your Ethernet Cable into your computer.
Once connected, open a web browser (IE, Safari, Chrome, Firefox) and go to netreg2.appstate.edu.
Log in using your App State credentials and follow the steps to register your device. You will need to reboot your device after 30 minutes for the registration to take effect.