Using Action frames is the first step to adding user interaction. By clicking on the
button, you will be prompted what type of action you want to insert. A play movie action will play the movie if a frame is reached and the movie is currently stopped. A stop movie action will stop the movie at the current frame. The jump to frame action will jump the movie to a specified frame. All actions are shown on the "Action Script" entry in the Cutting Room.
You can move these actions to any point in the movie, however, they cannot be resized, as they only take place during one frame.
Why use Actions?
If you had content later in the movie that you do not want displayed unless a user clicks a certain button, you can put a stop action to "pause" the movie until the user clicks on the button. You could then have the later section play, and once is finished, jump back to the paused section of the movie.