a lot of error

// Use this for initialization
void Start () {
    Cursor.visible = false;

    playerMovement = player.GetComponent<PlayerMovement>();
    playerHealth = player.GetComponent<PlayerHealth>();

    //prevent the playerMovement to move
    playerMovement.enabled = false;

    //prevent the birdMovement to move
    birdMovement.enabled = false;

    //prevent the followCamera to move
    followCamera.enabled = false;

}

// Update is called once per frame
void Update () {

    //if the game is not started and the player preses the spacebar then...
    if (gameStarted == false && Input.GetKeyUp(KeyCode.Space)

    //...start the game
    {
        StartGame();
    }


    //if the player is not alive...
    if (playerHealth.alive == false)
    //...end the game
    {
        EndGame();

        //...increment the timer to count up to restarting
        restartTimer = restartTimer + Time.deltaTime;

        //...and if it reaches the restart delay...
        if (restartTimer >= restartDelay)
        {
            //...then reload the currently loaded scene
            SceneManager.LoadScene(SceneManager.GetActiveScene().buildIndex);
        }
    }
}

private void StartGame()
{
    //set the game state
    gameStarted = true;

    //set the text color into invisible
    gameStateText.color = Color.clear;

    //allow the player to move
    playerMovement.enabled = true;

    //allow the bird to move
    birdMovement.enabled = true;

    //allow the camera to move
    followCamera.enabled = true;


}

private void EndGame ()
{
    gameStarted = false;

    //show the text game over
    gameStateText.color = Color.white;
    gameStateText.text = "Game Over!";

    //remove the player from the game
    player.SetActive(false);
}