// listen to when the mouse is pressed
addEventListener(MouseEvent.MOUSE_DOWN,downHandler);

funciton downHandler(e:MouseEvent):void{
// listen to when the mouse is released
stage.addEventListener(MouseEvent.MOUSE_UP,upHandler);
// listen to when the mouse is moved
stage.addEventListener(MouseEvent.MOUSE_MOVE,draw);
// set a random color and line width from 1 to 5
graphics.lineStyle(Math.random()*0xFFFFFF,Math.floor(Math.random()*5)+1);
// move line  to starting point of mouse
graphics.moveTo(e.stageX,e.stageY);
}
function draw(e:MouseEvent):void{

// draw line
graphics.lineTo(e.stageX,e.stageY);
}
function upHandler(e:MouseEvent):void{
stage.removeEventListener(MouseEvent.MOUSE_UP,upHandler);
stage.removeEventListener(MouseEvent.MOUSE_MOVE,draw);
}