Output plug polarity: The manufacturers of K'NEX have supplied adaptors for the 12v motor over the years which have either a "centre positive" or a "centre negative" polarity. The polarity determines whether the motor turns clockwise or anticlockwise. This probably does not matter for a Ferris wheel, but will make a difference if the motor is driving (for instance) a chain drive.
To attach the motor, first push rods through the two holes in the underside of the motor so as to connect it to the model, as shown.
Then place an axle across the front of the motor, so that the teeth of the white gear wheel engage with the worm gear on the motor shaft.