WoW:API UseAction

UseAction (ID,#{,target})

The first number is the action ID.

Each button on your action bar has an ID. The first button id is 1, and so on. There are 10 action bars in all, thus the highets action bar is 120.

The second number is either 1 or 0. The third number is optional and represents whether the action should be executed on yourself (1 = on yourself, 0 or nil, on your target or give you the spell targeting cursor). The default appears to be 0.