I have a fresh install of Ubuntu Server 20.04.1 on a Raspberry Pi 3 B+

I initially set it up connected via WiFi. I now plugged in an ethernet cable but I'm unsure how to tell which is currently the active connection via the command line. I'd prefer to disable the WiFi and have a wired connection.

I'd also like to know how to re-enable WiFi in the future in case I ever disconnect the cable.

I ran ifconfig -a and see the output for both eth0 and wlan0