show message on collision

Hello to all members of the forum.
I am a newbie in unity .
i have a script called boxTrigger and i want when a user collides with an object(cube) to show message…
How can i do it . With onGui? Please help…

using UnityEngine;
using System.Collections;

public class boxTrigger : MonoBehaviour
{
public Light light;
public Light light2;

// Use this for initialization
void Start () {

}

// Update is called once per frame
void Update () {

void OnTriggerEnter(Collider collider)
{
light.enabled=true;
light2.enabled=true;

}
void OnTriggerExit(Collider collider)
{
light.enabled=false;
light2.enabled=false;
}
}
// var mySkin : GUISkin;

// Assign the skin to be the one currently used.
//GUI.skin = mySkin;

// Make a button. This will get the default “button” style from the skin assigned to mySkin.
// GUI.Button (Rect (10,10,150,20), “Skinned Button”);

327533–11554–$boxtrigger_856.cs (701 Bytes)

All GUI code should be put in an OnGUI() method, yes.