A question i want to ask for general actionscripting!

look i am trying to learn how to use actionscript 3. i see the codes and sometimes i do get their pooint sometimes nope.

i can create buttons and some other things with actionscript 3 and i can create a basic webssite apart from the preloader.(which i hope you are going to help me pn my other topic)

now for my question.
what is the purpose and the use of packages and classes like this code

package
{
import flash.display.Sprite;
public class Starter_2 extends Sprite
{
public function Starter_2 ()
{
myTest();
}
private function myTest():void
{
var a:Suplemental_1 = new Suplemental_1 ();
a.thisTest ();
addChild(a);
}
}
}
import flash.display.Sprite;
import flash.text.TextField;
class Suplemental_1 extends Sprite
{
private var tField:TextField;
public function Suplemental_1 ()
{
}
public function thisTest ():void
{
tField = new TextField();
tField.autoSize = “left”;
tField.background = true;
tField.border = true;
tField.x = 200;
tField.y = 200;
tField.text = “Hello You, what is your name?”;
addChild(tField);
}
}

when we can manually add the textfield and customize it as we want through flash with the tools etc… i found a lot , almost all codes aropund are with these packages that try to import objects and things…why can’t we just place them import them and use their instances names for scripting ??? if i want to import them through the tools how can i script them to work like the packages do ?

i hope you giot the point of my question and i am waititng for your answers!!!