Adding GUI to this

Hi. I watched a YouTube tutorial about random numbers. But I he didn't add any GUI text to it. I tried doing it myself, but failed. What I wanted was a button which you could press. When you pressed the button, you got a random number pops up on the screen.

Here is the script he made:

var randNumber : int;

 function Update () {
     if (Input.GetMouseButtonDown(0)) {
         randNumber = Random.Range(1.0, 100.0);
         Debug.Log (randNumber);
         }
 }