Name button instances
You'll provide instance names for the buttons on the Stage so that you can refer to the instance names in ActionScript.
  - On the main Timeline, select the Content layer.
 
  - On the lower-right side of the Stage, select the button at the left. In the Property inspector (Window > Properties), type goScene_btn in the Instance Name text box to name the instance of the symbol.
    

   
  - Select the middle button and use the Property inspector to give the button an instance name of attachMovie_btn.
 
  - Select the far right button and use the Property inspector to give the button an instance name of playSound_btn.