Aim

Aiming is not an attack, it is a maneuver you do prior to a ranged attack that gives a bonus to your attack roll.
For each action point (second) you spend aiming, you get +2 modifier to the result of your ranged attack roll.
See Combat Rounds, Time and Actions.
You can spend a maximum of 2 consecutive action points aiming, for a maximum of a +4 modfier to your roll.
It is considered consecutive if you spend the last action point of a round aiming, and the first action point of the following round aiming, and then you shoot, provided you are not attacked in the meanwhile. If the latter happens, you lose the bonus you got in the previous round, and you only get the bonus achieved during the current round.