Start by cutting 1 piece of your main fabric 15in x 9in. This is going to be the piece you sew your pintucks into.

About 1 inch from the right, fold your fabric and pin

Sew as close to that edge as you can, If you need to you can change your needle position to the right so that you can get closer.

Fold and pin again about a 1/2 in from your first pintuck.

Repeat until you have a total of 7 pintucks on that side.

Now start at the other end of your fabric just like you did on this side, fold 1 inch away and sew 7 pintucks.
You should have an empty space in the middle.

Now you need to press the pintucks outward. the two sides of pintucks will be pressed opposite directions.

Now to find out what measurements to cut the rest of your fabric you need to lay the pintuck fabric on top of another piece of main fabric, cut it to match the size of the pintucked fabric. Do the same with your lining fabric so you should have 2 lining fabric pieces and 2 main fabric pieces.

Its time to sew on your snap

If you want to add a tag now would be the time to do it.

pin fabrics right sides together, the lining pieces with each other and seperate;y the main fabric pieces together.

The bottom edges of this bag are rounded off, in order to make sure I did this evenly I measured 1 inch from each corner like in the picture below, and marked it and thats where I turned when sewing.

sew along the sides and bottom with a 1/4 inch seam allowance. Leave 2 inches unsewn at the bottom of the lining fabric pieces. Trim the edges

Turn main fabric piece right side out and put it inside of the lining piece like this:

Pin and sew around the top with 1/4 inch seam. Turn everything right side out using the 2 inch hole in the lining and topstitch around the opening of the bag. You should have this:

Sew up the two inches on the lining and add a button if you wish.