Ammo HUD Script

Hello i’m making a fps and i’m noob at script so can you help me please?
i got a plane with a 3D Text on it ( Ammo Text ), it look like a HUD, and i want when i shoot with mouse1 the number of Text Ammo decrease.
Thanks !

In order for this to work you will have to make some things for the gun to shoot such as a bullet prefab, spawn point, shot sound, and bullet speed. if you already have a gun script then just use the ammo parts of this.

using UnityEngine;
using System.Collections;

public class Shoot : MonoBehaviour {
	public Rigidbody bulletPrefab;
	public Transform spawnPoint;
	public int speed;
	public float nextFire = 0.0f;
	public float fireRate = 0.1f;
	public int ammo = 150;
	public GUIText ammoText;
	public AudioSource shotSound;

	// Use this for initialization
	void Start () {
	// Update is called once per frame
	void Update () {
		if(Input.GetKey(KeyCode.Mouse0) && Time.time > nextFire)
			if(ammo > 0)
				ammo --;


	void Shot()
		nextFire = Time.time + fireRate;
		Rigidbody bulletInstance;
		bulletInstance = Instantiate(bulletPrefab, spawnPoint.position, bulletPrefab.transform.rotation) as Rigidbody;
		bulletInstance.AddForce(spawnPoint.forward * speed);


	void OnGUI()
		ammoText.text = "Ammo: " + ammo.ToString();