1. First, make your initial shape layer
2. Then create the shape that needs to be the "hole" on a separate layer.
3. Use your black arrow tool to select the "hole" shape.
4. Go to Edit>Copy
5. Turn off the visibility of your "hole" layer
6. Click on the grey mask of your original layer (in your layers palette.) You should see a little outline that appears around the mask once you click on it.
7. Go to Edit>Paste. This will paste the path of the "hole" onto your original layer. You now have two paths on the same layer.
8. While you are still selected on the "hole" path (if you aren't selected on it, use your black arrow tool to select it), then click on the "Cut our of Shape" option (in your options palette).
Your "hole" should now be cut out of your original shape.
