Action is when a person hits someone and the reaction is when that person hits him back. Action is when something does something and the reaction is when something else happens to the thing that did the action.

We did an experiment with a balloon, a straw, and two kids holding a string. You put the string through the straw, blow up the balloon, tie the end then tape the balloon to the straw. And you're ready for blast off! Let go of the balloon and it will go along the string until it is stopped by the kid's hand.