The first attack you make in a given turn has no penalty to hit. Each subsequent attack you make with that hand in the same turn incurs a cumulative -3 attack penalty to hit. Your attack penalty resets to 0 at the end of each turn. Attacks are typically associated with a hand. This could be the hand that uses a weapon, that casts a spell, or that performs an unarmed strike. If you are using multiple weapons in different hands, you can use the second for an Off-Hand Attack.