Need help getting the screen to fade.

I'm trying to get the screen to darken when I start the game and when I restart. I have followed a tutorial for this but was not very clear.

 public class ScreenFader : MonoBehaviour {
     
     // Holds the texutre to fill the screen
     [SerializeField] Texture2D fadeTexture;
     [SerializeField] Color colorStart = Color.black;
     [SerializeField] Color colorEnd = Color.clear;
 
     
 
     // Time to completion to fade
     [SerializeField]float fadeTime = 1.0f;
 
     // The container for the functions to be triggered when the fade has complete
     private event FadeCompleteEvent OnFadeComplete = null;
 
     // Defines the type of function which is used as a delegate
     public delegate void FadeCompleteEvent();
 
     // Internally used to track the passage of time
     private float timer = 0.0f;
     
     // Loads a prefab and create an instance from it
     static public void CreateFade (string _prefabName,
                                     FadeCompleteEvent _completeEvent) {
     // Load the asset as a basic object
     Object fadePrefab = Resources.Load(_prefabName, typeof(Object));
     
     // Create a new game object from the loaded prefab
     GameObject fadeObject = Instantiate( fadePrefab) as GameObject;
     
     // Find the fader's script component an assign the event
     ScreenFader fader = fadeObject.GetComponent<ScreenFader>();
     fader.OnFadeComplete = _completeEvent;
 
     }
     
     // Use this for initialization
     void Start () {
     
     }
     
     // Update is called once per frame
     void Update () {
         // Accumulate the passage of time
         timer += Time.fixedDeltaTime;
 
                   
         
         // Duration has been satisfied?
         if (timer > fadeTime)
         {
             timer = fadeTime;
         }
         if (OnFadeComplete != null)
         {
             OnFadeComplete(); 
             OnFadeComplete = null;
             Destroy(gameObject, 0.1f);           
         }
     }
     void OnGui() { 
       // Determine the passage of time as
       // a precentage of the duration time
         float percent = timer / fadeTime;
       
       // Use the percentage to the determine the
       // gradient between the two
         GUI.color = Color.Lerp(colorStart, colorEnd, percent);
       
       // Create a rectangle the size of the screen
       Rect screenRectangle = new Rect(0, 0, Screen.width, Screen.height);
       
       // Draw the texture filling the entire screen
       GUI.DrawTexture(screenRectangle, fadeTexture);
 
     }
 
   }

public class CoreGame : MonoBehaviour {

 [SerializeField] GameObject pauseMenu;

// Stores the current pause state; private bool paused = false;

 // Use this for initialization
 void Start () {
     ScreenFader.CreateFade("ScreenFadeUp", FadeUpCompleted);

     // Hide the pause menu intitially
     HandlePause(false);
 }
 
 // Update is called once per frame
 void Update () {
     // Exit early if paused
     if (paused)
     {
         return;
     }
     
     CheckInput();
     
     

 }
 static public void MakeChild(GameObject _child) { 
 
     GameObject coreGameObj = GameObject.Find("CoreGame");

     // Assign the child's transform's parent to the
     // recently found core game's transform
     _child.transform.parent = coreGameObj.transform;
 
 }
 void CheckInput()
 {
     // User has pressed pause?
     if (Input.GetKeyUp(KeyCode.P))
     {

         HandlePause(!paused);
     }
 }
 // Method to modify pause status
 private void SetPaused(bool _paused)
 {
     paused = _paused;

 }
 void FadeUpCompleted() {
     Debug.Log("Fade UP has completed!");
 }
 
 // Handles the actions of the pause event
 public void HandlePause(bool _pause) {
     
     paused = _pause;
      // Send a message to all children
         BroadcastMessage("SetPaused", paused);
         paused = !paused;
         Debug.Log("Pause Key has been pressed!");
         if (paused)
         {
             Time.timeScale = 0;
         }
         else
         {
             Time.timeScale = 1;
         }
         pauseMenu.SetActive(paused);
     }
 

}

public class PauseResume : MenuButtonBase {

 // reference to the core game object
 public CoreGame coreGame;

 // Call on button up
 protected override void doButtonAction()
 {
     coreGame.HandlePause(false);
 }


 // Use this for initialization
 void Start () {
 
 }
 
 // Update is called once per frame
 void Update () {
 
 }

}

public class PauseRestart : MenuButtonBase {

 // Called on button up
 protected override void doButtonAction()
 {
     ScreenFader.CreateFade("ScreenFadeDown", FadeDownCompleted);
 }
 
 // Use this for initialization
 void Start () {
 
 }
 
 // Update is called once per frame
 void Update () {
 
 }
 void FadeDownCompleted() {
     Application.LoadLevel("Project");
 }

}