Laura Thomas : Interactivity - Audio and points

put the project window into a single coloum layout this way was can drag sound onto the assets easily
select the explosion astorid pre fab and drag the explosion sound onto it in the inspector and select play on awake
do this for all explosions and then add the Shooting sounds onto the play game object in the hierarchy ( on the player game object deselect play on awake )
to get the shot sounds to play go into the game controller script and in the void update write audio.Play ();
then add background music to the game controller object and select play on awake and loop
then turn the volumes down to what sounds correct
create a new gui text and call it score text in the text box write score text and move it to the top left corner
open the game controller script and wrtie public GUIText scoreText private int score;

void UpdateScore ()
    {
        scoreText.text = "Score: " + score;
    }

 void Start ()
    {
        score = 0;
        UpdateScore ();
        StartCoroutine (SpawnWaves ());
    }

   public void AddScore (int newScoreValue)
    {
        score += newScoreValue;
        UpdateScore ();
    }

the script should now look like this

open the destroy by contact script and write

 public int scoreValue;
    private GameController gameController;

 void Start ()
    {
        GameObject gameControllerObject = GameObject.FindWithTag ("GameController");
        if (gameControllerObject != null)
        {
            gameController = gameControllerObject.GetComponent <GameController>();
        }
        if (gameController == null)
        {
            Debug.Log ("Cannot find 'GameController' script");
        }
    }