This documentation assumes you have some experience installing Debian, that you will work from a Debian machine to perform this install, and that you have purchased and correctly assembled your PC Engines APU2.
Credits: This gist came from this teklager.se guide and this custura.eu guide.
Caution: This process will write over existing data on your APU2. Make sure to do any necessary backups of your data.
I believe that the APU requires non-free firmware. As of this writing, that means downloading firmware-11.0.0-amd64-netinst.iso.