Nikon FM2 Film Plane back removed

Film Winder top left with stem down through camera
Used to hold film magazine, and keep film flat along film plane, also used to rewind film after exposers are taken.
This particular SLR requires you to engage a release to lift the winder upward to insert or remove film magazines, if you don't engage the release, you may break the winder lock.

Viewfinder center SLR means single lens reflex, what you see is what you get looking through whatever lens is attached to the 35MM camera flash mount on top of viewfinder
most modern slr's show the shutter speed and F stop in the viewfinder as well

Top right, Shutter speed dial, Film ASA/ISO dial ajusts for different film speeds and for different shutter speeds.
Also on top far right is the Film Advance lever, after each shot this must be wound to advance the film across the film plane for the next exposer.