Pretty much by the instructions on the site. I downloaded the distribution, extracted and wrote the image on the 4GB SD card, inserted that into the RPi and powered up. I already had an entry in my DHCP server for the Ethernet interface so it appeared at a known IP address. I ssh'ed in and let it update itself to the latest release, then configured it. Similar to Rasberry Pi OS, it's configured using a ncurses/dialog interface.
So, nothing to see here, let's move on. Only additional things I did were to install the wiringpi, ntpd, gpsd, nfs-client and autofs packages. The last two are to mount an NFS directory from my workhorse so that I can backup configuration information.