There are many ways to turn a ski, and they nearly always depend on either unweighting or steering, or as usually happens, a combination of both. There is also a third alternative, where you lie down on your back in the snow, swivel both skis around in the air, and your bottom too, and you find you are facing the other way when you stand up...
Unweighting - The Down Slow & Up Slow Method
You go down slowly, and then jump the backs of the skis up. As they unweight, you can get them round. The jump becomes minimal once you have got the hang of it, and the faster you go, the less you have to unweight the skis. By the time you read this, you should be well past this stage, and will probably be doing very little unweighting. This method of unweighting is used when learning parallel turns, doing linked short turns in deep snow, and by downhillers and giant slalom skiers with slight variations.
Unweighting - The Down Quick & Up Quick Method
If you drop down on the skis towards the end of a turn they will actually unweight and come off the ground. If you don't believe me, stand on a weighing machine (preferably without skis and boots unless you have a large bathroom), and drop down very quickly. The dial will drop to zero before it comes up again to register more than your normal weight. As you drop down quickly while finishing the turn, the skis become unweighted, they slide round a little further (rather like a miniature christie stop). The weight on the skis goes back up again as you rise up and brake against the snow, the skis should follow, and you jump them up and round.
This is a far more effective method than the first for certain turns, but it is harder work. It is used by slalom racers, flash Harrys on the piste, and on hard steep slopes back country skiing. You will also be doing it once you have digested 'The Basic Short Turn' technique. Do not worry if you do not understand this method just yet; it will be made clear later.
Unweighting - The Moguls or Bumps Method
The bumps unweight the skis for you! As the middle of the skis pass over the top of a bump, both the back and the front of the skis come off the snow, or at least will be only lightly touching it. The skis can therefore be pivoted round on their centrepoints, if you do certain other things as well that are discussed in the article 'Better Bumps Technique