Need help: basic turret game (no packages)

I need to make a turret-like game for a school project due Tuesday. Different monsters are supposed to pop up at random on the screen, and you have to shoot them down. They can’t pop up within a 50 pixel radius from the turret, and they will only stay on the screen within a given time limit before they disappear, and they must give points when they’re killed.
I have to explain the code to the teacher. I don’t know or understand packages at the moment, so I’m trying to make the game without them. I understand everything else, I’m just not good enough to come up with the code.

My problems are making the laser that come out of the turret travel across the screen, not making the monsters pop up inside the 50 pixel radius away from the turret and putting the monsters in an array and removing them from the array after they’ve been shot and giving points for them.

My code is crap and lacking a lot. I’ve been trying to get things to work for a long time, but I’ve failed every time I’ve tried, so there’s not much to work with. What I need is some pointers on the problems mentioned above.

Any help at all on any of the problems would be really really awesome!

stop();

var x1:Number;
var y1:Number;
var a:Number=0;
var b:Number=0;
var skuddfart:uint=10;
var teller:Timer=new Timer(300);
var monsterTeller:Timer= new Timer(3000);
var monsterArray:Array = new Array;
//skudd.x = kanon.x;
//skudd.y = kanon.y;

//makes the monsters spawn
startKnapp.addEventListener(MouseEvent.CLICK, startSpill);
function startSpill(evt:MouseEvent) {
    monsterTeller.addEventListener(TimerEvent.TIMER, monsterTellerF);
    monsterTeller.start();
    startKnapp.alpha=0;
}

//places the monsters at random locations
function monsterTellerF(evt:TimerEvent) {
    trace("i monstertelleren:",b);
    for (b=0; b<2; b++) {
        trace(monsterArray);
        var fiende= new monster();
        x1=Math.random();
        y1=Math.random();
        x1=x1*1000;
        y1=y1*1000;
        x1=Math.round(x1&550);
        y1=Math.round(y1%400);
        fiende.x=x1;
        fiende.y=y1;
        addChild(fiende);
        monsterArray.push(b);
    }
}

//rotating the turret
stage.addEventListener(KeyboardEvent.KEY_DOWN, rotering);
function rotering(evt:KeyboardEvent):void {
    if (evt.keyCode==37) {
        kanon.rotation=kanon.rotation-10;
    } else if (evt.keyCode==39) {
        kanon.rotation=kanon.rotation+10;
    } else if (evt.keyCode==40) {
        //trying to see if it will make the monsters disappear
        monsterArray.pop();
    }
}

//a timer trying to make the lasers fire across the stage
teller.addEventListener(TimerEvent.TIMER, tid);
function tid(evt:TimerEvent) {
    a=a+1;
    trace("a:",a);
}

stage.addEventListener(KeyboardEvent.KEY_DOWN, skyting);
function skyting(evt:KeyboardEvent) {
    //skudd.rotation=kanon.rotation;

    //shooting the sprite lasers
    if (evt.keyCode==Keyboard.CONTROL) {
        var avfyr=new laser();
        avfyr.x=a;
        avfyr.y=a;
        addChild(avfyr);
        avfyr.rotation=kanon.rotation;
        teller.start();

    }
}