I suggest renting equipment from a sporting goods store before buying. Some stores will apply part of the rental toward the purchase of new. Shops that rent cross country skis and boots sell their inventory for pennies at the end of the season.
There are skis for prepared tracks, for breaking your own trail (a little wider and longer so you float better in new snow), and for backcountry where you'll be skiing fast downhill (better edges for turns). The slightly wider models are best to start with.
Even if you know how to ski alpine style, take a lesson to get the basics of cross country down before you set out on your own.
You work up a sweat while skiing, so the clothes you wear are surprisingly light. But when you stop, or if the weather changes, you can get chilled very fast. Be sure to take along a jacket, food and drink, and a space blanket (one of those lightweight mylar emergency ground covers) when you travel away from the ski area.
Most cross country skis today have a pattern embossed in the area under the foot (the fish scales mentioned above) that provides traction when you press down and push yourself forward. Some skis depend on properly applied wax to stick when weighted, yet glide when unweighted. Differences of only a few degrees in the temperature of the snow require a different wax scheme. A well-waxed ski is magic!
