Open the zip by half. With the right side of the paper facing you put your zip facing down along the top edge of the bag, centre the zip so there are equal amounts of overhang at either end.
If using paper outer do not use pins as they will make in holes in the paper. If you have small clips or paper clips these would be useful to hold in place whilst you take it to the sewing machine.
Using a zipper foot, sew the zip in place with a 0.5cm seam allowance and using a slightly larger stitch on your sewing machine. You will need to move the zip head out of the way when you get to.
Do this by ensuring your needle is down in the fabric, then raise the presser foot and wiggle the zip head past the presser foot, lower the presser foot and carry on to the end.