To get full functionality, Mark had to download (which includes the Epson Scan 2 utility). After that, the printer appeared twice in the print dialog – one AirPrint, one Epson. He chose the Epson one.
Linux users often struggle. The ET-2850 isn’t fully open-source friendly, but Epson provides for Ubuntu, Debian, Fedora, etc.
A printer driver is a small piece of software that acts as a translator.