Summarize this article in one sentence.
After you have the desired number of tulle layers, sew the layers together along the stitched edges to connect them. A zigzag stitch works best to connect your tulle layers securely. Line up the ribbon edge with the edge of the tulle on one side and pin along the edge. Make sure that the ribbon overlaps the edge of the tulle by about 0.5 inches (1.3 cm). The ribbon should also have an equal amount of excess on either side of the tulle skirt edge so you will be able to tie the ribbon in a bow. Fold the ribbon over to the other side of the tulle and pin along this edge to hide the raw edges of the top of your tulle skirt. Sew along the pinned edge to secure the ribbon. Remove the pins as you go. If you want to secure the tulle skirt with elastic instead of ribbon, line up the elastic and the top edge of the tulle skirt on your sewing machine so that the ends are even. Begin sewing a zigzag stitch down the length of the elastic.  Tug the elastic slightly as you sew to ensure that it is the same length as your skirt edge, but do not stretch the elastic beyond the edge of the skirt. Sew all the way to the end of the elastic and tulle skirt. Stitch the ends of the elastic and tulle skirt together to secure them in a circle. Your skirt is ready to wear after you sew the ribbon into place. You do not need to sew a seam on the bottom of your tulle skirt because tulle does not fray. You can leave it unhemmed and it will be fine.

Summary:
Sew the tulle layers together with a zigzag stitch. Pin the ribbon onto the pleated edge of the tulle. Fold and sew the ribbon onto the tulle edge. Sew the tulle onto your elastic strip. Leave the bottom of the skirt unhemmed.