No power other than your fingers. Its chucked in the drill to keep it straight for the tap. You use your fingers to turn it as you tap and let it pull down into the material.
Its nothing more than a tap handle except you don't have to look to see if it is going in straight, that is done by the shaft that is chucked in the drill. The blue handle slides freely up and down on that shaft.
And you are right, sometimes the simple thing is the hardest to see what is going on.