What makes the whole thing go is the electric motor in the starting motor.  Here are the parts.

This installs into the transaxle and the gear meshes with the flywheel which turns everything.

You can see the wires, covered in sheathing, that plugs into the stand.  In the stand base is a motor speed controller and two connections, one that goes to the starter and one that accepts a 12v transformer input.

The transaxle bolts to the stand and then the engine bolts to the transaxle.