I'm a newbie too so this might not be totally right, but what I have got, mostly from here is LR is not really live. It contains organisims that are living. Bristleworms, pods, etc. other forms of bacteria and plant life grow on these rocks as well. All of these things are an essential part of the natural biological filter in a salt water system. They all contribute to the break down of waste and it's removal.
The standard estimate I see most often is 1-2 lbs per gallon of water in the tank.
It's easy to find out more, just look through back threads, it's brought up often.
Also; LR needs to be cured, time to get rid of the die off which causes ammonia and nit's in your tank. This can take any where from a week to a month or longer, even most "cured" LR from your LFS (local fish shop) still needs some ammount of curing although consideribly less.
Good luck and enjoy.
Pease people, correct me if I'm wrong.