You'll need popsicle sticks (also known as craft sticks). You need 159 sticks total.
These are what I used. I recommend the same (or similar) size, not the wider craft sticks since they're shorter and the shelf won't be as wide.
You'll also need glue — white glue or a hot glue gun — and scrap paper (or a little cup or something, for the glue).
Start by gluing six sticks together, layered as shown.
Glue on another layer of sticks, and keep going till you have 10 layers in each section.
Make two of these.
If the last step's directions confused you, this photo should explain it better.
Attach the shelves by gluing four sticks to the sides. (Note: I accidentally ruined the shelf I'd been making for this post, so the rest of the tutorial shows the first I made which is why it's finished in these pictures.)
IMPORTANT! When attaching the shelves, make sure the top sticks face the same direction (see photo)
or the sticks creating the back won't lie flat.
Choose which side is the back, glue sticks as shown. Make sure the ends all touch so there's even spacing.
If you used white glue, put the shelf somewhere for a couple hours so the glue can completely dry. If you used hot glue, proceed to the next step.
Hold the finished shelf to where you want to hang it, and use a pencil to mark where you'll hammer in two nails or thumbtacks. (I recommend nails if you'll be putting anything heavy on the shelf.)
Remove the shelf and hammer in your nails, leaving about half an inch to hang the shelf from.
(I used L shaped ones for extra support so the shelf can't slide off the wall.)
Gently hang your shelf. If you used L shaped nails like I did, they should slide right in between the sticks.
Here's what your finished shelf should look like!
Final measurements are approximately 12½" x 8½" x 1¾"
Now you can fill it with whatever you want!
You can also use this to store bottles of nail polish.