N/m2 means how much surfaces can be loaded, i.e., the pressure (Newton per square meter) the surface can withstand.
1670 N/m2 means (1670/9.82 kg/m2) i.e., 170 kg/m2
Max c-distance 1200 etc means that the maximum distance between roof trusses can be at most 1200 mm (1.2 m) if the snow load is 101 kg on a square meter, i.e., a little less than half a meter of snow cover.
D-ram and U-ram I'll leave to someone else...
