If you want to ski down the mountainside, you'll need to make your way to the top of it first. Jump on Glacier Express and enjoy the ride.
When you've spent a bit of time at this mountainside transportation system in Val-d'Isere, why not check out Lac de Tignes, La Daille Ski Lift, and Le Fornet Ski Resort? They're not far from Glacier Express and also a hit with travelers.