Android Touch Cube on screen , level To Load

I search for 6 days on forums but I can’t do this: I have a 3d object, for example a Cube on the screen. If I touch this, load a new level.
They written It’s easy with raycast. But I dont know raycast. Please help.

I don’t have much experience with raycast, but something like this might work:

var ray = Camera.main.ScreenPointToRay (Input.mousePosition);
var hit : RaycastHit;
 
if (Physics.Raycast (ray, hit, 100))
Debug.DrawLine (ray.origin, hit.point);

if (hit.transform.name == "The Cube's Name...")
Application.LoadLevel(1);