While this MAN video doesn't go into a complete description for the switch you're talking about, it does give enough information for a different model to give you an answer.
This switch does control the transfer case for on-road (right part of the dial) and off-road (left part of the dial) driving. The different positions of the switch tells the transfer case what interlock you desire. Just as @WeatherVane stated in the comments, the images with the angled tires are the front end. Looking at the images, where you see the bulge is where the interlock happens. The first image with the bulge in the center is where both front and rear wheels are supplied power. The one where the bulge is to the front ensures the interlock provides power to the front of the vehicle. The one to the rear is for rear interlock. The transfers on these vehicles are all-wheel drive (AWD) units, so power is supplied to all four all of the time. The interlock switch ensures power goes to both, front, or rear as needed. If the computer senses the vehicle doesn't need the interlock, say while traveling down the highway, it will automatically disengage it regardless of what position the switch is in. The center two positions would allow for completely automatic, allowing the computer to decide the interlock without driver intervention.