Whether you buy a zipper at the fabric store or use a roll of zipper "tape", the steps for inserting a zipper are really very simple. You need a zipper foot for your sewing machine. This how-to shows you how to insert a home dec sort of zipper used in cushions, pillows and slipcovers. The zipper I am inserting here is 40" long and will be the back band or boxing on a window seat cushion.
What you need:
sewing machine with zipper foot
fabric you're inserting the zipper into
What you do:
1. cut a strip of fabric 2 inches wider than the remaining boxing
For a 5 inch thick cushion, boxing is cut at 6 inches, allowing 1/2" seam allowance on both sides. The piece of fabric used for the zipper is cut at 8" and cut in two, lengthwise.
2. pin two 4" pieces of fabric together, right side to right side and stitch using the longest basting stitch on your sewing machine
3.lay zipper on open seam with zipper teeth placed directly on top of stitches
4.pin in place and begin stitching at one end, stitching straight all the way down side, stop, pivot and stitch up the other side
5. when finished, backstitch cut thread
6. add zipper tab onto zipper, moving tab down on zipper to open it and get it working
7. fold a scrap piece of fabric in two, making a tab to stitch at top of zipper to keep it from coming off
8. flip zipper section over and using small scissors or seam ripper, cut through the basting stitches so zipper is functional
9. set aside to sew into cushions or pillows
If you need to know how to fix a zipper, this ManMadeDIY article covers it in great depth.