I plan to put the Ubiquiti main station where my time capsule currently is. So I assume I'll just plug one of the time capsule ethernet ports into one of the Ubiquiti ethernet ports and it will be all set.
As far as a physical connection, you would connect an Ethernet cable from one of the four LAN <--> ports on the Ubiquiti router to the WAN "O" port on the Time Capsule.
Then....you will need to reset the Time Capsule back to factory default settings and the set it up to work with Ubiquiti router. The setup will consist of two main parts.....a basic setup, to get the TC working in a normal way with the Ubiquiti router, then some tweaks.....like turning off the WiFi on the Time Capsule, since you probably won't need another wireless network.....(unless you want to use the TC WiFi for guests, so you don't need to give the guests the password for your private Ubiquiti network.
Time Machine will also need to be reset on your Mac if you plan to back up over the Ubiquiti wireless.
As we mentioned above, we are happy to provide step-by-step instructions if you need them, but we would need to know what device......a Mac, etc.....that you will be using for the setup. If it is the MacBook Pro that you mention in your profile.....is the Mac still using the El Capitan operating system, or have you upgraded to a more recent version of the operating system?
A step-by-step setup won't really be of much use though.....until you have the Ubiquiti system set up and working. That is why we suggested that you get the Ubiquiti mesh system working......before.....you try to set up the Time Capsule.
It is not feasible to try to set up the Time Capsule to work with Ubiquiti router in advance......before you you have the new mesh system set up and working......if that might be what you are thinking.