How do you decipher the 30 codex pages in assassins creed 2

Go to Leonardo DiVinchi to decipher them. If you have done that after finding them and talking to him. Then go back to where youre Uncle Mario's Kingdom is and go into the room in the back on the first floor right side. The wall where his other pages were, interact with them and then use eagle vision. Afterwards start turning the pages around to form a map.