Using to the UMBC Residential Network (ResNet) with a Mac is straightforward; first, you'll need to find your Mac's wired ethernet address (MAC address).
From the Apple menu, select About this Mac, then click "System Report" or "System Information". Select "Network" from the list on the left, then click on the wired network adapter you're using ("Ethernet", "Thunderbolt Ethernet", "USB Ethernet Adapter", etc.). Look for "MAC Address" in the list of information displayed.
Alternatively, you can open System Preferences, select Network, then pick your network adapter you're using from the list on the left, then click Advanced, and click the Hardware tab.
Once you have the MAC address handy, follow the instructions in How do I register my device for use with the Residential Wired Network at UMBC?
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 How do I exempt my computer from the Residential Network firewall? for more information.