Tammi,
Just to elaborate a little on the live rock, it is basically base rock of the coral reef that comes straight from the ocean and is encrusted with whatever was living on it at the time it was collected: feather dusters, polyps, coraline algae, etc. People want live rock because it makes their aquarium look natural and it provides biological filtration. Live sand can be thought of similarly, except that it is obviously sand that came from a reef area that is also full of life.