I have cannon and aim dot.

Aim dot should be even exactly in mouse cursor position. Cannon should look to aim.

I don't know how to have aim right under mouse cursor. I don't know how to rotate cannon to look at aim.

I have read some others question / answers about Raycast to object make looking on mouse position.

But i cannot make it works.

edit(moved from "answer")

NOw i have this, and this works, but not like i want, i need aim to be right under mouse. Don't understand how to use World coordinates of mouse, when i try my aim gets right to camera coordinates. When i try viewport coordinates ScreenToViewportPoint, my aim not under mouse too.

var cannon : GameObject;
var aimSight : GameObject;
var aim : GameObject;
var speed = 2;

function Start(){
    aim = Instantiate(aimSight, transform.position,transform.rotation);
}

function Update () {    
    //mp.x = Input.mousePosition;
    var mp = new Vector3();
    mp.x = Input.GetAxis("Mouse X") / speed;
    mp.y = Input.GetAxis("Mouse Y") / speed;
    mp.z = 0;
    //wmp = Camera.main.ScreenToScenePoint(mp);    
    Debug.Log(mp);
    aim.transform.position = new Vector3(aim.transform.position.x + mp.x, aim.transform.position.y + mp.y,mp.z);
}

Please help me (((