Registering a command to a key

stage.addEventListener(KeyboardEvent.KEY_DOWN, keyUsed);  // or use KEY_UP

function keyUsed(event:KeyboardEvent)
{

         nextFrame();  // or prevFrame();
}

You will need to add an event listener first:

stage.addEventListener(KeyboardEvent.KEY_DOWN, keyDownHandler);

and then define the function

function keyDownHandler(e:KeyboardEvent):void

{

     switch(e.keyCode)

     {

          case Keyboard.W:

               // do something

               break;

     }

}

That would define a command to the W key. The Keyboard class has many constants for keys.