My understanding is that when you rotate the stick, the angle controls the rotational (yaw) speed of the Volcopter (in other words, you hold the stick straight, it'll keep looking in a fixed direction, say north. Now if you twist the stick a few degrees, it'll slowly rotate in that direction (and keep rotating as long as you hold it twisted). If you twist it more, it'll rotate faster. If you let go (untwist), it'll stop rotating and maintain that heading.)

You can see this in this video of the first manned flight a year ago, at around 2:26.

You can also nicely see the thumb controlled ascent/descent switch at the beginning. Controls look super intuitive.

https://www.youtube.com/watch?v=OazFiIhwAEs