In another post I did a quick video on processing the cubes on the AX2012R2 demo VM. This video is the same overview but on the AX2012 R3 demo VM because the operating system was updated to Windows 2012 R2 and SQL 2014.
Keep in mind if you are running the demo VM on a laptop or machine that has just average hardware this process could take a while to run.
Cheers
Lachlan