Make sure you don’t measure the tulle to the skirt; you measure it to your waist or hip measurement, wherever the skirt will sit.
Measure the waistband to your body, and sew it in a loop.
Pin the waistband to the top of the skirt. You can either have it flat on one side, or fold it over to cover both sides.
Sew it together, making sure the tulle, the skirt and the waistband all line up.
Be careful not to catch extra tulle up on top of the waistband.
You now have a fluffy skirt.