To connect the power and turn on the motor, attach the alligator clip to the terminal at the end of the battery housing. When not in use, keep the alligator clip attached to the frame of the motor for safety. Be aware that this motor can rotate very fast. Watch your fingers!
Notably, this device was not a product of the St. Louis Motor Company, nor of someone named Louis; its developer, S. A. Douglass, was a turn-of-the-century high school teacher in St. Louis, Missouri. You can learn a bit more about the history of this design from the Kenyon College site at physics.kenyon.edu/EarlyApparatus/Electric_Motors/St._Louis_Motor/St_%20Louis_Motor.html .