Check out the official (more in depth) howto at readthedocs or on github. If you run into troubles, contact us by mail, irc or simply open an issue on our github issue tracker. Our contact info is listed in the howto, as well.
Grab an embedded system - a Raspberry Pi will do, but something faster -> More fun! Of course, you can also use the machine you're using to read this or any other.
Install a rather recent version of Debian, Arch or whatever you think you can handle on the RPi
Add a few dependency software bits from your Distribution. Namely mongodb (>=3.2), nodejs & npm, GDAL binaries and a few Python3 parts.
Install the source code
Run the manage tool to set up provisions and build the frontend for the first time (we have no released frontend tarballs, yet) - Beware: This step will take a rather long time on a Raspberry Pi! Do it in a screen session...
Visit the RPi in your favourite web browser and add an account simply by logging in for the first time. (You can add and change accounts with the manage tool, as well)