Completed sling. If you poke a hole through the cloth to attach you cords your sling will come apart however if you fold and attach the cords as shown this is a great way of making a quick and effective sling for throwing stones of any size or shape. A sling used for throwing large projectiles should have a larger pouch and at some point you might want to use a wrist anchor instead of a finger loop.
The grid shown is 1inch by one inch. Size is personal preference. This is a good and average size for a sling pouch.
Fold your material, doubling it over like this will add to the structural strength.
Make a small hole through all thicknesses of material where they fold over. Push a loop of cord through the hole as shown then tuck the end of the pouch through the cord loop and pull these cords tight to anchor your sling's cords to the pouch.
Use a smaller diameter cord, thread or string to bind/whip the ends of your cords together completing the sling.
A hole in the pouch will help in keeping your projectile seated until you throw it. It may take a little trial and error but for the most part if you have basic crafting skills, a piece of cloth and string/cord you can make this sling in a few minutes.