Liverock is called live because it has living things in and on it. When it's shipped to you they usually ship it in wet newspaper like yours was. During shipping some of the living things are not going to make it and die. If you put this liverock into your tank without curing it first the dead things degrading is what cause the ammonia spike. Since you don't have any living creatures in your tank already that's ok but once you do get fish and whatnot in there after the tank cycles you won't want to put more liverock directly in the tank because the ammonia going up can harm or kill your fish so you "cure" it first.
Basically curing liverock means putting the rock into a large container of some kind, covering it with saltwater mixed just like you'd put into your tank, scrubbing it often to remove any of the dead things, and keeping a powerhead for water movement, heater, and thermometer in the container to keep the things still alive on the rock living. The rock is "cured" when there's no more dead things on it, it should smell like clean saltwater and not rotting something or the other icky, and is then safe to add to your tank.