Cross country skis are are much wider, intended to reduce ground pressure. Downhill skis are narrower, to reduced resistance, and intended more for packed snow.
skis are waxed to reduce the friction with the snow and therefore if there is less friction then the skis will go faster.
Ski wax lets the skis glide over snow.
Friction between skis and snow may be reduced by waxing the skis. Air friction is reduced by tucking the body into a streamlined position.
To distribute the mass of the skier and thus reduce frictional drag.
Spread the weight over a larger area. For a human: snow shoes, skis For a vehicle: bigger wheels, treads
Wax to make it simple is slippery, this when placed on the skis reduces the friction between the snow and the skis, (yes there is some friction between skis and snow). The less friction, the faster your skis can glide across the snow, and the faster you go.
Snow + Ancient Footware = Skis
I believe it has something to do with the large surface area resulting in lower pressure on the snow (or whatever your skiing on, if not snow) so you don't fall into the snow.
Skis and snowshoes spread a person's weight out so that they do not sink.
The larger the surface area the more pressure can be spread out, therefore it is less likely to fall through the snow. As pressure = f / a.