Step 1: When you started out skiing, you were taught to snowplow! Apply that to skiing backwards.
Step 2: Now to initiate your turn:
If you want to turn to the right, try standing as tall as you can and point with your left arm exactly to the spot you want to turn to. When you finish your turn you'll bring your arm back, and look up at the slope for a split second. Now look over your right shoulder and point with your right arm in the exact direction you want to go. Turn right turn left repeat, turn right turn left repeat.
Step 3. As you get more comfortable you'll notice a tendency to have a lead change with your skis (meaning the downhill ski while in a turn will be leading the turn, a stagger in other words) when you get to that point, work on your flexibility and you'll be carving switch as well as your carve forwards.
Hope this helps.