How to add a Gui skin to script

i want to add in a gui skin to this script

using UnityEngine; using System.Collections;

public class HUD : MonoBehaviour { public PlayerVitals pv; public Weapon wep;

 // Use this for initialization
 void Start()
 {
     if (!GetComponent<NetworkView>().isMine)
     {
         this.enabled = false;
     }
 }

 // Update is called once per frame
 void OnGUI()
 {
     if (GetComponent<NetworkView>().isMine)
     {
         GUI.Label(new Rect(20, Screen.height - 40, 100, 40), "Health: " + pv.hitPoints.ToString("F0"));
         GUI.Label(new Rect(20, Screen.height - 20, 150, 40), "Ammo: " + wep.bulletsLeftRead + " / " + wep.bulletsPerMagRead + " | " + wep.magsLeftRead);
     }
     else
     {
         this.enabled = false;
     }
 }

}