According to Tiggs:
Accuracy does two things:
- Determines probability of hitting the target.
- If your accuracy is greater than defensive skills of your target, you do additional damage.
Level difference between the player and the target also has an effect on hitting and damage done.
Your accuracy increases with skill mods associated with the weapon type. For example, your general ranged accuracy will improve as you learn Marksman skills, improving your chance to hit the target while wielding a ranged weapon.
It is unclear whether posture still has an effect on accuracy.