You will need leather about 1mm thick. About a 2 ½" x 2 ½" piece should work.

If you are using a F1 you will want a veg-tan leather, other machines can do any leather you'd like.

Once your three pieces are cut, take the smallest part and glue it to one of the other pieces on the backside. Make sure you line up your hole. 

This will give our piece a slightly puffy look.

Now sandwhich your pieces together and preform a saddle stitch all the way around.

Now take your edge beveler and shave off the edges.

Once that is done you can use a sanding block or paper and even up your edges.

Finish off with a burnished edge. 

Take a 3/16th eyelet and set it into your hole. This will reinforce your hole.

Finally engrave your favorite band on the front and add your keyring.