[mwcard=DNQ05]Libro Mortuos[/mwcard] is a spawnpoint, which from the codex is defined as an object with the ability to cast spells for you.
Also from the codex, "You select spells for your Spawnpoints during the Planning Phase, at the same time that you choose spells for your Mage to prepare (one additional spell for each Spawnpoint)". So basically you take an extra spell and place it by the Spawnpoint, in this case, Libro. Then, during your deployment phase you may cast that spell and ONLY that spell.
Hope that answers what you were asking.