The idea is that you ride the board like a surfboard, rather than a snowboard. On a snowboard your weight is on the front foot. On the snowsurfer it's on the back foot, like surfing. So you just jump on and assume a knees-bent surfing pose and they reckon within an hour you'll get the hang of it and be carving. You also use the upper body more than on a snowboard.The principle is straightforward. The bottom ski is a carving ski, so you move from edge to edge very fluidly. Moving your weight on the larger top board (set 90mm above the ski) has a greater effect on the angle of the ski, which gives you easy turns without too much effort.
The snowsurfer doesn't come cheap though. £249 for a "quick release" top deck and truck to attach to any ski. £499 for the complete deal. Comes with a leg-rope so you don't take somebody out with a runaway ski.
See the video and more here - snow-surfing.com