Well, I now understand that you mean the two "button controls" right above the shuttee dial in the corner.
Actually these are no buttons or controls, but caps, covering female sockets.
The left one (with the flash-symbol) is connected to a shutter contact (as with a still camera) closing when is full open. By this you gain a synchronisation to use a flashlight when the camera is set to single-frame mode. This can be used for stop-Motion Animation or takes at very low ambient lighting.
The right one (with that two-reels symbol) is connected to the release contact. By this starting and stopping a tape-recorder during the take. Thus one can use the unedited audio-tape together with an unedited movie. The tape-recorder needs to have a remote control socket/contact.
This does NOT gurantee lip-synchronous audio-recording, though Nikon speaks of synchro-contact. This would either need a link between the motors of the camera and recorder or motors each frequency controlled to highest degree.