When it comes to hunter shots, the Attack Power or (AP) I will talk about is Ranged Attack Power. Your AP can be boosted by items with +Agility and items with +Attack Power. For every +1 to Agility, you will gain +2 Ranged Attack Power (in addition to other benefits). For clarity:
Before patch 2.0.1, hunters received 2 RAP per agility, whereas after they receive 1 RAP per agility. However, this is slated to be changed back to 2 AP along with the release of Cataclysm.