Everything is ready to let the player drop his/her disc. You can check whether each column represents a legal move or not, and you know which row will occupy a falling disc, given a column.
The idea: When the player clicks the mouse, we check if the column he picked is a legal one, in this case we place the disc in the proper row and let the other player move. At the moment, there isn't a computer-controlled opponent yet, so you will have to play both with red and yellow discs.
The development: To make the player drop the disc with a mouse click, you have to import MouseEvent class in disc_movieclip.as to use your old friend MouseEvent.CLICK listener.
import flash.display.MovieClip;
import flash.events.Event;
import flash.events.MouseEvent;
You also need to know which player is playing through all classes, so add a new variable to class level variables.
private var currentColumn:int; private var currentPlayer:uint; private var par:Main;
currentPlayer will store the number...