Making a Prism

Now you need to make a new layer, so go to "layers" and then "new raster layer"

Now we're going to make the octagon look a little more realistic.  Go to the "Effects" menu, then "3D effects", then "cutout"

In the Cutout dialogue box, you need to choose the following settings:

Verticle:  -4
Horizontal:  -4
Opacity:  60
Blur:  40 
Shadow colour:  black
Fill interior with colour:  checked
Fill colour:  white

Now we need to do the same again but with different settings, so go to "Effects", then "3D effects" then "cutout" 

and use these settings:

Verticle:  6
Horizontal:  6
Opacity:  100
Blur:  40 
Shadow colour:  black
Fill interior with colour:  checked
Fill colour:  white

Now we need to deselect it, so go to "Selections" and "Select none"

We need to get rid of the white bit in the Octagon now, so go to your layers palette and right click on layer 2 then click on the "delete" option

Save your work