Aaaargh...
After an 11 hour drive back from photokina and at 00:45 AM I can manage only simple answers. Google it!
But briefly, the 'body' holds slow, fine grain positive film. You put your neg under the trapdoor and contact print that onto the FG pos. The 'wind on' can advance half a frame (there's an 18x24 mask) or with two clicks, a whole frame.
And so to bed...
Cheers,
R.