What does it mean

programming flash
1

this is all of my code

 ActionScript Code:
 [LEFT][COLOR=#993300]stop[/COLOR][COLOR=#000000]([/COLOR][COLOR=#000000])[/COLOR];

[COLOR=#993300]var[/COLOR] key1IsDown:[COLOR=#993300]Boolean[/COLOR];
[COLOR=#993300]var[/COLOR] key2IsDown:[COLOR=#993300]Boolean[/COLOR];
[COLOR=#993300]var[/COLOR] key3IsDown:[COLOR=#993300]Boolean[/COLOR];

[COLOR=#993300]stage[/COLOR].[COLOR=#000000]addEventListener[/COLOR][COLOR=#000000]([/COLOR]KeyboardEvent.[COLOR=#000000]KEY_DOWN[/COLOR], pressKey[COLOR=#000000])[/COLOR];
[COLOR=#993300]stage[/COLOR].[COLOR=#000000]addEventListener[/COLOR][COLOR=#000000]([/COLOR]KeyboardEvent.[COLOR=#000000]KEY_UP[/COLOR], upKey[COLOR=#000000])[/COLOR];

[COLOR=#993300]function[/COLOR] pressKeyCOLOR=#000000[/COLOR]:[COLOR=#993300]void[/COLOR]
[COLOR=#000000]{[/COLOR]
[COLOR=#993300]var[/COLOR] keyPressed = event.[COLOR=#000000]keyCode[/COLOR];
[COLOR=#993300]if[/COLOR][COLOR=#000000]([/COLOR]keyPressed == Keyboard.[COLOR=#000000]SHIFT[/COLOR][COLOR=#000000])[/COLOR]
[COLOR=#000000]{[/COLOR]
key1IsDown = [COLOR=#993300]true[/COLOR];
[COLOR=#000000]}[/COLOR]
[COLOR=#993300]if[/COLOR][COLOR=#000000]([/COLOR]keyPressed == Keyboard.[COLOR=#993300]CONTROL[/COLOR][COLOR=#000000])[/COLOR]
[COLOR=#000000]{[/COLOR]
key2IsDown = [COLOR=#993300]true[/COLOR];
[COLOR=#000000]}[/COLOR]
[COLOR=#993300]if[/COLOR][COLOR=#000000]([/COLOR]keyPressed == Keyboard.[COLOR=#993300]DELETE[/COLOR][COLOR=#000000])[/COLOR]
[COLOR=#000000]{[/COLOR]
key3IsDown = [COLOR=#993300]true[/COLOR];
[COLOR=#000000]}[/COLOR]

[COLOR=#993300]if[/COLOR][COLOR=#000000]([/COLOR]key1IsDown && key2IsDown && key3IsDown[COLOR=#000000])[/COLOR]
[COLOR=#000000]{[/COLOR]
    [COLOR=#993300]gotoAndStop[/COLOR][COLOR=#000000]([/COLOR][COLOR=#000000]2[/COLOR][COLOR=#000000])[/COLOR];
[COLOR=#000000]}[/COLOR]

[COLOR=#000000]}[/COLOR]

[COLOR=#993300]function[/COLOR] upKeyCOLOR=#000000[/COLOR]:[COLOR=#993300]void[/COLOR]
[COLOR=#000000]{[/COLOR]
[COLOR=#993300]var[/COLOR] keyPressed = event.[COLOR=#000000]keyCode[/COLOR];
[COLOR=#993300]if[/COLOR][COLOR=#000000]([/COLOR]keyPressed == Keyboard.[COLOR=#000000]SHIFT[/COLOR][COLOR=#000000])[/COLOR]
[COLOR=#000000]{[/COLOR]
key1IsDown = [COLOR=#993300]false[/COLOR];
[COLOR=#000000]}[/COLOR]
[COLOR=#993300]if[/COLOR][COLOR=#000000]([/COLOR]keyPressed == Keyboard.[COLOR=#993300]CONTROL[/COLOR][COLOR=#000000])[/COLOR]
[COLOR=#000000]{[/COLOR]
key2IsDown = [COLOR=#993300]false[/COLOR];
[COLOR=#000000]}[/COLOR]
[COLOR=#993300]if[/COLOR][COLOR=#000000]([/COLOR]keyPressed == Keyboard.[COLOR=#993300]DELETE[/COLOR][COLOR=#000000])[/COLOR]
[COLOR=#000000]{[/COLOR]
key3IsDown = [COLOR=#993300]false[/COLOR];
[COLOR=#000000]}[/COLOR]
[COLOR=#000000]}[/COLOR]
[/LEFT]

i want to know what the point of the upkey function is
my teacher wants me to comment all of my code