basics:
CA : Current ability
PA: Potential ability
200 current ability would be the best player ever ( zidane, ronaldinho, Henry all have around 185-190 current ability )
200 potential would be the best prospect ever ( the higher the potential, the more chance they have of turning into superstars. Rooney, Reyes, Robinho would all be around 180 potential ability)
Current ability and potential are the key stats, this is basically there ability. Once you have decided a players ability, adjust there stats to how you want them. The stats are second behind the ability