OnClick open URL

I am using C# and I would like my button to open a URL once it is clicked. How do I write this?

using UnityEngine;
using System.Collections;

public class OGSButton : MonoBehaviour {

// Use this for initialization
void Start () {

}

// Update is called once per frame
void Update () {
          Application.OpenURL("http://unity3d.com/");
}

}

Is it a unity UI button?
If so you have to make a public void in your script, which opens the url, just like you did above.
If you want to activate the void on a button press you have to:

  1. go to the button.
  2. scroll to the bottom.
  3. where you see the onclick stuff, add the object that contains the object with your OGSButton and select the void that needs to be called.

Detailed tutorial here: Unity - UI Button