Need help with my gun script!

I made a shooting script but when I shoot the gun it shoots really fast and it shoots a lot of bullets at once. I only want it to shoot one bullet every time. Here is my script.

using UnityEngine;
using System.Collections;

public class Shoot : MonoBehaviour {
	public Rigidbody bulletPrefab;
	public Transform spawnPoint;
	public int speed;

	// Use this for initialization
	void Start () {
	// Update is called once per frame
	void Update () {
			Rigidbody bulletInstance;
			bulletInstance = Instantiate(bulletPrefab, spawnPoint.position, Quaternion.identity) as Rigidbody;
			bulletInstance.AddForce(spawnPoint.forward * speed);

And could somebody tell me how to make it where the bullet doesn’t go on it’s side. When I shoot the bullet goes forward but the bullet will face down.

static Quaternion identity;

The identity rotation (Read Only). This quaternion corresponds to “no rotation”: the object."

Try doing this:

bulletInstance = Instantiate(bulletPrefab, spawnPoint.position, bulletPrefab.transform.rotation) as Rigidbody;