What can I do to make my game work? I don't know what to do.

using UnityEngine;
using System.Collections;
using UnityEngine.UI;

public class GameState : MonoBehaviour {

    private bool gameStarted = false;
    [SerializeField]
    private Text gameStateText;
    [SerializeField]
    private GameObject player;
    [SerializeField]
    private BirdMovement birdMovement;
    [SerializeField]
    private FollowCamera followCamera;
    private float restartDelay = 3f;
    private float restartTimer;
    private PlayerMovement playerMovement;
    private PlayerHealth playerHealth;

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

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

        // Prevent the player from moving at the start of the game
        playerMovement.enabled = false;

        // Prevent the bird from moving at the start of the game
        birdMovement.enabled = false;

        // Prevent the follow camera from moving to it's game position
        followCamera.enabled = false;

    }

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

        // If the game is not started and the player presses the space bar...
        if (gameStarted == true && Input.GetKeyUp (KeyCode.Space)) {

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

        }

        // If the player is no longer alive...
        if (playerHealth.alive == false) {

            // ...end the game...
            EndGame();

            // ...increment a timer to coun up to restarting...
            restartTimer = restartTimer + Time.deltaTime;

            // ...and if it reaches the restart delay...
            if (restartTimer >= restartDelay) {

                // ...then reload the currently loaded level.
                Application.LoadLevel (Application.loadedLevel);

            }

        }

    }

    private void StartGame () {

        // Set the game state
        gameStarted = true;

        // Remove the start text
        gameStateText.color = Color.clear;

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

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

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

    }

    private void EndGame () {

        // Set the game state
        gameStarted = false;

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

        // Remove the player from the game 
        player.SetActive (false);

    }

}