How to create a pop-up window on mouse click?

I’m relatively new to scripting so I apologise if this is a silly question. I’ve got a scene set up with multiple cubes that are interactive. They change colours when my crosshair hovers over them and when you click the left mouse button, it loads up a new scene.

My question is, how would I change this setup to have a pop up window appear on mouse click instead of a new level loading (and possibly disappear on a 2nd mouse click)? I’ve been messing around with the script but I’m not sure which script I should be editing to enable this pop up window.

My raycast script is as follows:

public class selectObject : MonoBehaviour {
	public RaycastHit hit;

	// Use this for initialization
	void Start () {
	
	}
	
	// Update is called once per frame
	void LateUpdate () {
		Ray ray = Camera.main.ScreenPointToRay (new Vector3 (Screen.width / 2, Screen.height / 2, 0));
		if(Physics.Raycast (ray, out hit, 5)) {
			if(hit.collider.gameObject.GetComponent<interactHighlight>()!= null){
				hit.collider.gameObject.GetComponent<interactHighlight>().OnLookEnter ();
			}
			if(hit.collider.gameObject.GetComponent<mehScript>()!= null) {
				hit.collider.gameObject.GetComponent<mehScript>().OnLookEnter ();
			}
	
			if(hit.collider.gameObject.GetComponent<mehScript2>()!= null) {
				hit.collider.gameObject.GetComponent<mehScript2>().OnLookEnter ();
			}

		
}
}
}

And the interactHighlight scripts all follow this structure:

public class interactHighlight : MonoBehaviour {
	public GUIText target;
	private bool selected = false;

	// Use this for initialization
	void Start () {
	
	}
	
	// Update is called once per frame
	void Update () {
		selected = false;
	
	}

	public void OnLookEnter () {
		renderer.material.color = Color.red;
				target.text = "Left Click to See More Information";
				selected = true;
		}

	void OnGUI () {
		Event e = Event.current;
		if(Input.GetMouseButtonDown(0) && selected) {
			Application.LoadLevel ("2_levelTest");

		}
	}
}

What would I have to change to enable a pop up window? Thanks in advance

Are you looking for our own custom window within the game? or are you looking for a message box with ok | cancel buttons? If your looking for the first one which i assume you are, see this