Bottom of Nikon FM2

left see the motorwinder head where the motorwinder mounts to wind the film via an electric motor.
the button below that is pushed in after the roll of film has been exposed to allow you to rewind the film, it is a safety device to ensure the film stays advanced and dosen't slip backward.
The hole right of center is threaded to allow you to mount the camera on a tri pod to steady it for timed exposures or distances with telephoto lenses.

the screw to the right is for the two stacked batteries much like a watch battery, the batteries in the FM2 serve only one function for the on board light meter since it is a manual only camera.

the four contacts on the far right are to be used with the motorwinder for the electrical contacts to tell the winder when the shot was taken to advance the film correctly.