I’m not a mac guy, so I don’t know how helpful this will be. Perhaps one will respond with more helpful info.
Did you install the CI tools? This is where the ASIO driver (or the mac equivalent) for the interface is located. It’s always best to ignore the disk that came with the product and download the latest version from the mysteinberg web site.
Did you plug in the interface and wait until the system recognized it BEFORE starting your DAW software?
Are you using Cubase? If so, did you set the system up in Devices/VST Connections (or choose one of the CI Templates on opening a project in Cubase)?
The mic input is NOT a MIDI signal. It is audio. Completely different, and handled differently by the system.
Hopefully this will be enough to get you started.