When you engage the autopilot, it should enter a roll hold and pitch hold mode. Then use the scroll wheel on the middle of the black knob to control pitch up.down. Each scroll click is roughly 1/4 of a degree in pitch change from what I've seen.
There is an IAS hold mode as well, once you have your pitch set and autopilot engaged, you can click IAS and it is supposed to maintain that IAS for the climb, but its a little wonky - I'm going to submit a bug. You can then use the middle of the black knob to control the set IAS speed which indirectly controls your v/s.