One thing I was surprised to learn is how easy it is to program in ActionScript. It's pretty much just like a compiled version of JavaScript, with a few slight improvements. One thing to keep in mind, however, is the output is a SWF file rather than an EXE, and the "application" is very graphically oriented: I'm not even sure if you can make an ActionScript application that has no GUI. So, our basic HelloWorld application is as follows:

package {
    import flash.display.Sprite;
    public class HelloWorld extends Sprite {
        public function HelloWorld( ) {
            graphics.beginFill( 0xFFCC00 );
            graphics.drawCircle( 40, 40, 40 );
        }
    }
}