Getting my movie clip to jump and stay on stage

For an assignment and just to let you know I am a newbie.

My stage size is 640x 480y

I have placed an image of a chicken on my stage over the background and (with help) I have moving clouds.

I have gotten to move my chicken up, down, left and right using the arrow keys.

I can get it to jump on its own but then I can't seem to assign it to a specific key.

I also can't seem to keep it on the stage.

import flash.display.*;

import flash.events.*;

          /* created a container containing an instance

             of my background image & used addChild to

             place it one the stage*/

var myBackground:BackGround = new BackGround();

    addChild(myBackground);

          // Moving clouds//

var myCloud:MyCloud;

         //Created a loop that pushes 6 clouds to the stage//

for (var i:Number = 0; i<6; i++)

{

    myCloud = new MyCloud();

      addChild(myCloud);

        /*Creates a random value varible containing

          Math.random() which returns a number 0 <=

          And <1 so,will never get 1*/

    var randomValue: Number = Math.random()*1;

        /*Creates a random collection of clouds drawn

          moving in various positions of the stage width.

          And the x & y Scale of the clouds are set randomly*/      

     myCloud.x = Math.random()*stage.width;

     myCloud.scaleX = myCloud.scaleY = randomValue;       

         /*Creates an event for the myCloud to listen out for

           function to get the MovieClip (all clouds) flyby when

           entering the frame*/

    myCloud.addEventListener(Event.ENTER_FRAME, flyBy);

    function flyBy(event:Event):void

{

          // Modular function for all the clouds to move//

    MovieClip(event.currentTarget).x +=6;

    if (event.target.x> stage.stageWidth)

    {

        event.target.x = 0;

    }

}

    addChild(myCloud);

}

// The Hen and Key Board functions //

var myHen:ChickHen = new ChickHen;

addChild(myHen);

//The x and y positioning co ordinates for the hen//

myHen.x = 230;

myHen.y = 350;

var distance:int = 100;

//leftmost position based upon boundary box

var leftArrow:int = (myHen.x - myHen.width /2) + 100;

//rightmost position based upon boundary box

var rightArrow:int = (myHen.x + myHen.width / 2) - 100;

//topmost position based upon boundary box

var upArrow:int = (myHen.y - myHen.height / 2) + 100;

/* Add keyboard listeners to the stage */

stage.addEventListener(KeyboardEvent.KEY_DOWN,move);

function move(event:KeyboardEvent):void

{

/* Use a switch to determine which key was pressed */

var key = event.keyCode;

switch(key)

{

case 39:

myHen.x +=distance;

break;

case 37:

myHen.x -=distance;

break;

case 38:

myHen.y -=distance;

break;

case 40:

myHen.y +=distance;

break;

}

}

I used the following method to make it jump  but I don't know how to assign this to a specific key:

stage.addEventListener(KeyboardEvent.KEY_DOWN, jump);

stage.addEventListener(KeyboardEvent.KEY_UP, land);

function jump (event:KeyboardEvent): void

{

  myHen.y -=120

}

function land (event:KeyboardEvent): void

{

  myHen.y +=120

}