Hi, I've got such a machine although it is in unusable condition. I think it works like this: for flash you choose an aperture (you see the corresponding DOF arrows move) the front ring will show a red line with flash bulb sign. If you move the rings (actually it is 1 ring) to the "yellow"position (sun symbol) you see the DOF arrows move again: you can choose your DOF; you don't see an aperture number and the camera will choose a shutterspeed automatically. If you align the meterneedle with the index, exposure shoukd be good ( that is when it works; mine doesn't). There is one ring "in between". You can move that after pressing the button on the left, to set the filmspeed. Hope this helps.
Cheers, Jan