Move block to click

To make the cube go to the position of the mouse you can do something like this:

 public Transform cube;
 public Camera cam;
 void Update(){
 if(Input.GetButtonDown("Fire1"){
 Ray ray = cam.ScreenPointToRay(Input.mousePosition);
 if (Physics.Raycast(ray))
                 cube.position = transform.position;
 }
 }

Now, i dont quite get the "when the cube comes to a position, continues to move on". Are you using a navmesh agent on it?