mouse position on tag

Ok so you're almost there right. Look at where this would fit in. You cast a ray, but then you want to check out what it hit before doing anything else. So you hit a collider, it belongs to a gameObject, you want that tag :

 if(Physics.Raycast(ray,hit,200)){
     
     // What did i hit ?
     Debug.Log( " I hit tag : " + hit.collider.gameObject.tag );

then to check a condition of something , use if

 if ( hit.collider.gameObject.tag == "TagImLookingFor" )
 {
     // now I hit the tagged object fore sure !
 }

put it all together

 var bullet : Transform;
 
 function Update () {
     if(Input.GetMouseButtonDown(0)){
         var ray : Ray = Camera.main.ScreenPointToRay(Input.mousePosition);
         var hit : RaycastHit;
         if(Physics.Raycast(ray,hit,200)){
             // What did i hit ?
             Debug.Log( " I hit tag : " + hit.collider.gameObject.tag );
             if ( hit.collider.gameObject.tag == "TagImLookingFor" ){
                 // now I hit the tagged object fore sure !
                 Instantiate(bullet, hit.point, Quaternion.identity);
             }
         }
     }
 }