For visual learners, this video from Lauren's Top Tops shows the standard centered zip method, while this video from Professor Pincushion covers the process of installing a zipper in a seam. To make sure this fits your project, are you: (clothing) or a bag ?
Once secure, carefully remove the basting stitches in the middle of the seam to reveal the zipper. Finishing Touches lb.zip
Pin the fabric pieces right-sides together and sew from the bottom up to the marked point where the zipper opening begins using a regular stitch. For visual learners, this video from Lauren's Top