For something ksp-like, I guess the easiest is to press "play" on the Pluto scenario on the left. Note the hints in the top left. Trying it myself now, it seems the scenario is set quite quickly, so I'd set the simulation "steps per run" to maybe 5, and the thrust should be something on the order of 1 (I thought the scenario data should have set that appropriate to the craft but apparently not)
Edit: oh yeah and it expects arrow keys and a scroll wheel, there is no button overlay implemented for mobile yet