You can put a zipper in your pillow in four sewing steps. Really, it is that easy. I learned this method from Jane Hewitt, a local sewing instructor. For a 16" square pillow, you will need:
Fabric (Cut 2 squares 16" x 16" and one rectangle 16" wide x 4" high - seam allowances ARE included. You want your finished pillow to be slightly smaller than the insert. Trust me, it'll look so much better.)
Pillow Insert (16" square)
Zipper to match (14" long)
Thread to match
Rotary Mat and Cutter (useful, but not necessary)
Let's get to it.....