You can Aid someone in combat: Aid Attack or Aid Defence. To Aid Attack, make an attack roll vs. DC 10. If you succeed, you grant a Circumstance bonus +2 to attack. In this case, you distract targets from properly defending themselves. To Aid Defence, you roll an attack vs. DC 15 and success grants a Circumstance bonus +2 to Defence. In this case, you actively defend your comrades from harm, parrying blows that they missed. Combat Aid requires a standard action. You can enhance this manoeuvre with the Team Player feats.