A skirt can have many types of openings. But the best one is the kind with zippers. You can attach the zippers to the skirt in many ways. Here are the ones I know.
3 ways to sew a waistband with zipper
Method 1 With the waistband and invisible zipper
In this method an invisible zipper is attached to the skirt from the waistband to the hip level.
Step 1 Complete the skirt body.
Keep the 2 pieces of the skirt (back and front pattern pieces of the skirt) right sides together and stitch the side seams. The red lines in the picture is the stitching line. 7 inch is left un-stitched on the top edge of one side seam to insert invisible zipper
Turn the skirt right side out.
Step 2 Attach the waistband piece to skirt
Cut out the waistband first – you need a piece measuring the top edge of your skirt. I have taken a width of 3 3/4 inch for a waist band – the final width of the waistband will be 1 1/2 inch.
Keep the waistband piece on top of the top of the skirt, right side down on the right side up skirt. The top edge is joined together with a 1/4 inch seam allowance.
Step 3 Invisible zipper
You need to cut the invisible zipper to measure 11 inches long. Do not forget to close the bottom end of the zipper with stitches across the zipper teeth- or they will come open.
Step 4 Attach invisible zipper
Keep the zipper open. Align the zipper face down on one open edge. The zipper should be kept 1/2 inch up from the waistband seam.As you keep the zipper remember to fold the short edge to the outside as in the picture .Baste stitch in place .
Do so for the other side as well
The seam allowance inside should be turned up as you baste stitch.
On the first edge, just use an invisible zipper foot to stitch the invisible zipper very close to the teeth.
Step 5 Fold the top of the waistband down. Still the skirt is face up, allright?
Stitch along the seam allowance joining the waistband
Use a zipper foot for this.
Now just flip the waistband inside out and your waist band is almost ready
Step 6 Top stitch the zipper edge
You have to stitch the zipper from the top along the zipper teeth so that everything is finished well. You can hand stitch as well.
Step 7 Finish the waistband
Fold the back edge to the inside and pin in place. Stitch in the ditch from the front or hand sew in place from the back.
You can find the full skirt made here in this post on making an Aline skirt.
Method 2. With facing
The other alternative is to sew the skirt with a facing in place of waistband – Here you will attach the zipper to the skirt body and then finish the top edge with a facing.
The facing is cut in the shape of the top edge of the skirt.
Join the facing pieces for the front and the back.
Attach the facing to the top edge of the skirt.
Flip to the back of the skirt and then stitch it here. Hand sewing is preferred for this.
You can read more about this in this post on making a mini skirt here.
Method 3. With waistband and buckle
This involves a waistband with one end overlapping the other end of the waistband and then closing the opening with a buckle. The zipper is attached to the skirt and not to the waistband.
You will be sewing a simple zipper insertion here.
The waistband is made and joined to the skirt.
You can read more about this in this post on making a Pencil skirt
Or in this post on sewing a waistband for a Skirt.