The Ethernet cable connects to your router, the router provisions the RPi with an IP address.
In one of your earlier posts you said you had Ethernet access for this unit in your office, while WiFi should also work, the RPi case you chose is not optimal for WiFi as it does not have a lot of openings for the radio signal to get inside where the WiFi antenna is located on the board.
WiFi might still work OK, but it will be a function of how far away you are from the router.
But first you need to get it setup using Ethernet, then you can switch it to WiFi if need be, for that you just need it to get an IP, then you can access it's local web page via a web browser, either by entering the IP itself, or the above mentioned .local address.
I don't think there is much of any setup that needs to occur using the unit's local web page (other than the WiFi config), the actual configuration as an endpoint occurs in your Roon interface itself. A DAC must be connected via USB for that.
Here you go @Olson_jr