Spoilers Don't read if you aren't completely frustrated:
After starting the engine you need to adjust the throttle and mixture. Release the breaks as well. (although there isn't much flying mostly uncontrolled tumbling)
but how do you start the plane
Spoiler again with step by step instruction:
Congratulation you basically experienced an accurate simulation of starting an actual Cessna engine. I wanted to make some achievements that would have given you hints on the necessary steps, by rewarding you for making the correct steps, but I spent way too much time on the mouse over feature.
The other buttons are read hearings and mostly turn on lights and blinkers. They are optional and only consume electric charge.