Cannot get Time Capsule to back up via ethernet

Hello, I'm having some trouble getting a Time Capsule to perform an original backup via ethernet. The Time Capsule is in an apartment with only wireless (no modem or router in the apartment) and the wireless is pretty spotty, so it would be nearly impossible to perform the full backup via wifi. I am able to connect to the Time Capsule via wifi but when I plug it into the MacBook via ethernet and turn off wifi on the computer the computer cannot see the Time Capsule. How exactly do I set up the Time Capsule to perform the first backup via ethernet cable, and subsequent backups via wifi?

Is the WAN port different than the ethernet ports on the Time Capsule? I may have been plugged into that, because when I connected them via ethernet only they weren't talking.