Bag width is zipper width + 3"
Bag height is about 2/3 of width
Seam allowance in the image is 1/2" but I'm actually sewing them at 5/8"

Cut out two pieces of cloth from the template


Put the cloth together good-side to good-side
Sew a baste line along one long-edge
(Straight stitch, long and loose, do not anchor either end)


Iron the seam flat so the the cloth is spread to the left and right
The good-side of the seam is exposed upward


Place the zipper opening-side-down over the seam
So that the zipper opening aligns with the basted seam
Pin the zipper in place

Note that the zipper pull-tab is tucked in, pointing in the direction of the pull


Sew a button-hole stitch from the edge of the seam to the start of the zipper mechanism
(zigzag stitch, 0.75 length, 3 width, 3 tightness)
Sew such that both sides of the seam are secured together

For the pull-tab end of the zipper, sew inward to where the pull-tab will be but don't sew over the zipper parts yet

Put zipper foot on sewing machine
Check how to adjust the needle to the left or right such that you can continue using the zigzag stitch and the needle does not collide with the foot

Sew from before the start of the zipper, in a straight line, all the way along the outer edge of the zipper, till past the end of the zipper
(zigzag stitch, 0.75 length, 3 width, 3 tightness)

Do this on both sides of the zipper


The seams look like this from the good-side


Use a seam-ripper to remove the baste seam
This will reveal the usable side of the zipper


If there is a gap at the pull-tab end of the zipper

Then open the zipper several inches to get the pull-tab out of the way
Flip the cloth over to good-side-down
And button-hole-stitch the middle seam to come in right to where the zipper actually starts
Include the zipper's lose ends in this seam, pulling them to lie together right up to where the teeth start
(did not save a pic of this)

Flip the cloth to good-sides-together
Align the short-edges together on the side with the zipper pull-tab
Cut a short length of ribbon, pinch its ends together, and pin them in between the sides of cloth
This will create a loop of ribbon, anchored in the side of the bag, that will stick out so that a label can be attached to it

(view from the opposite side)


Pin the entire short-edge together
And pin along the other short-edge also
Sew a baste line along each short-edge
(Straight stitch, long and loose, do not anchor either end)


For each basted seam,
Trim away the top layer of fabric to 1/4" from the baste seam


For each basted seam,
Fold the lower layer of cloth over so that it's edge is along the baste line
Iron it in place


For each basted seam,
Fold the edge inward one more time, along the baste line
Iron it in place


For each basted seam,
Sew a loose zigzag along the whole edge, close to the inner edge of the folded cloth
(zigzag stitch, 3 length, 3 width, 3 tightness)


Leave the zipper half-open so that the bag will be easy to turn inside-out

Sew a baste line along the open long-edge of the bag

Cut the corner off of each end of the remaining open long-edge of the bag
Such that when the last edge is folded up and sewn, the corners will be secure (no holes or gaps left)


Repeat the steps for trimming, folding, ironing, and sewing the last long-edge of the bag
Same as was used on the two short-edges of the bag

Turn the whole bag right-side-out

The bag is complete

This example was done with a thin cotton cloth
If the cloth is thick (like duck canvas)
Then when folding the non-zipper edges
- Do trim the upper layer of cloth
- Do fold the lower layer over to touch the baste line
- Don't fold again, it will get too thick to sew easily
- Sew the zigzag along this edge and just manually remove any loose threads