How do I use my Gold Skulls?

#1

I used the guide to get a couple of gold skulls from the strange monument (respect to those that solved the puzzles!) How do I see how many skulls I have and how do I use them?

#2

You can trade books in the same location where you get gold skulls.

#3

Thanks for that - I am pretty certain I tried clicking on those ??? and got no response - it works now. However I have discovered that the character I was using was corrupted so perhaps that is why I was getting weird behaviour.