Throw Object from Camera and Mouse Position

Unity Engine
1

I am trying to write a script which throws a Ball from your Camera, but flies to the direction of you cursor (Crosshair). I can not get it to work though…
What I am trying to build is the same as the throw in this game:

This is what I have got so far:

void FixedUpdate () {
        if (Input.GetButtonDown("Fire1")) {

            Vector3 mousePos = Input.mousePosition;
            GameObject projectile = Instantiate(Input.mousePosition.x, Input.mousePosition.y, transform.rotation) as GameObject;
            projectile.GetComponent<Rigidbody>().AddRelativeForce(new Vector3(0, 0, 2000));
        }
    }

It seems to throw my Ball right from the middle of the Screen, but you can not control it by mouse position.

2

mousePosition returns a point in screen space… you need to convert that into world space.