Click and add blocks on a platformer.

Hey all,

I'm trying to create a 2D platformer game where you can click on the screen and create a block where you clicked. This will all be on a 0 Z axis. This is the code I have so far attached to an empty game object:

 var block : Rigidbody;
 var level: GameObject;
 
 function Start()
 {
     level = GameObject.Find("Level");
 }
 
 function Update () 
 {
     if(Input.GetMouseButtonDown(0))
     {
         var pos = Input.mousePosition;
         pos.z = 0;
         Debug.Log(pos);
         clone = Instantiate(block, pos, transform.rotation);
         clone.transform.parent = level.gameObject.transform;
         Destroy (clone.gameObject, 3);
     }
 }

I tried using a code similar to a first person shooter bullet code. I'm a little bit new to Unity but I understand what's going on with the code so far, I need to translate the Mouse's X and Y value into the screen's so it will place the blocks accurately. Any suggestions?

Thanks.