[Jotmo]

You put current through the coils, that makes magnetism, which pulls on a permanent magnet, which causes rotation.

Not all electric motors have magnets, but they all work using coils and magnetic fields.

So in this case, how is the electric field applied to the rotor? And why would you need pistons to do that?

Not expecting you to answer that, just wondering.

[Fichori]

I would speculate that the magnetism pulls the rotor around much in the same fashion that expanding gases or air would push it around.

I'm afraid I'll have to see better drawings before I even start to understand it.

Here's something I can understand...
(Blue-green object on the right is a valve)

(Untested idea for firing pellets with compressed air in a center fire rifle.)