First, you take one piece of fabric you like for the outside.
( I glued a piece interlining on it, so the fabric would be stronger)

Then you take a piece of interlining and draw a rectangle on it that is a little bit shorter than the zipper.
(Like the light lines)
And in the middle of the square another line and on the sides a triangle
(Like the darker lines)

(This is not a new zipper I bought, but I cut it out of an old sportbag)

You take a piece of another fabric you want to use for the inside of the zipper-bag.
and stitch it with the piece of interlining like this
!Only stitch the purple rectangle!
<
Make sure the piece of fabric is not in the middle of the fabric of the zipper-bag (below)

Like this
<<<

This will become the zipper-bag.
And the black fabric is going to be the big messengerbag.

Now you cut the black lines and fold and pin the sides like this.

Then you sew a rectangle, so it will look like this
<<<

Sew the zipper in a rectangle on the fabric.

Then sew your other piece of fabric(dots) for the bag on the other piece(dots).
!Don't attach it to the black fabric!

Tah-daah!
Your zipper-in-a-bag is finished!

*Go to
<a href="http://www.cutoutandkeep.net/projects/messengerbag_with_painting">here</a>

to see how you make the messengerbag*