Attention: Iím not a teacher.
Thatís simple enough.
doing something [uncountable] the process of doing something, especially in order to achieve a particular thing
The government must take action now to stop the rise in violent crime.
What do you think is our best course of action?
They met to discuss a plan of action.
something done [countable] something that someone does
Her prompt actions probably saved my life.
The child could not be held responsible for his actions (=he was too young to be blamed for them).