Cams change the pumping efficiency of your engine, and typically shift your power curve around. The more aggressive a cam is, the less efficient your engine becomes at lower RPMs (but becomes more efficient at higher RPMs).
Major factors of a cam:
Duration
Lift
Split
Duration is how long the valve is open, measured in degrees of crankshaft rotation starting and ending at 0.050" valve lift. This is typically the advertised duration you see. Lift is the maximum valve lift accomplished, which can also change with your rocker arms depending on what ratio they are. The rocker arms multiply the lift of the cam lobe (I believe the LS3 uses 1.7 rockers). Split (or lobe separation aka LSA) is how far apart the center lines of the intake an exhaust lobes are, again measured in crankshaft degrees. A byproduct of duration and LSA is overlap, which is how long both the intake an exhaust valves are open. Overlap typically dictates drivability of a cam. This is a very watered down explanation.
I've got too much else going on to write up about forced induction right now.
