Write an article based on this "Slide elastic into gap in waistband seam. Sew the elastic ends together. Close the open edge of the seam. Finished."
To finish your skirt, you will need to add the elastic to the waistband. Slide your elastic piece in through the gap that you left in the waistband at the beginning. Then, use your fingers to work the piece through the entire waistband.  It can take a while to work the piece of elastic through the waistband. Attaching a safety pin to the end of the elastic before you insert it into the waistband may help you to pull it through a bit easier. After you have pulled the end of your elastic through the other end of the waistband and it is going all the way around the waistband, sew the two ends of the elastic together. This will secure the elastic in a circle inside of your fabric waistband. After you have sewed the two ends of the elastic together, close the opening in the fabric waistband by sewing the gap closed. After the gap is closed, you can trim away any excess thread and your skirt is ready to wear!