Using to the UMBC Residential Network (ResNet) with a Mac is straightforward; connect your computer to the network jack in your room with an ethernet cable, and your computer should display a login box:
Enter your UMBC username and password and press OK. Your computer should be online in a few seconds. If you've left "Remember this information" checked, then your computer should automatically sign in whenever you plug into a network port.
If you are running software that is blocked by the normal ResNet firewall, you can register your computer to be exempted from the firewall. See $ARTICLE for How do I exempt my computer from the Residential Network firewall? for more information.