1 and 2 are intertwined but you can still play 2 without playing 1. Characters from one make appearences but not to much more than that. 3 is a prequel to 1, but again, you don't need to play 1. 4 and 5 take place in completely different universes.
Call of Duty Points (CP) are the in-game currency that can be used in Modern Warfare to obtain new in-game content for use in Multiplayer and Special Ops game modes.