Pull and release

I’m creating a game where I want to pull the ball and then release it, so it can fly towards the wall.
Kind of an effect like you can see in angry birds.

Here is a little bit of code:
What I want is that you really see that pulling effect from the original position, now I’m just grabbing it.

private bool release = false;
    private bool hold = false;
    private int pulledAmount = 0;



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

    void OnMouseDown(){
        Debug.Log ("Klik");
    }

    void OnMouseDrag(){
       
        pulledAmount += 1;
        Vector3 pz = Camera.main.ScreenToWorldPoint(Input.mousePosition);
        pz.z = 0;
        GameObject.Find("Ball").transform.position = pz;
    }


    void OnMouseUp(){
        Debug.Log("Drag ended!");
    }

Unity has a tutorial on making angry birds type game. There are two parts I think to it and they include free assets that you can experiment with. This may help you get on the right track.

Yea I saw that one already, but this type of things I will not really learn, checking my code and telling me what can be improved and how would be better I guess.