You will need something to get you ski to stick to the snow to provide traction for you to push off of. There are two ways this is accomplished. Some skis are smooth along the total length of the ski. The skier applies kick wax to the bottom of the ski under the foot. When the skier puts weight on the ski the wax sticks to the snow and allows the skier to push off.
Waxable skies are faster than waxless skies under most conditions.
However, you have to use different types of wax for different temperature ranges and snow conditions. If you are going to use your skis for backcountry travel most of the time and plan to do some camping or mostly camping with your skis I would suggest getting waxless skis. They are less hassle to deal with and you do not have to bring along a bunch of different kick waxes when you go out. However, if you like tinkering with you skis and think that you will really get into skiing you might want to get Waxable skis. Especially if you will we doing some skiing on groomed trails, because they will be faster on a groomed trail.