Open up the PlayerBehaviour script. In the top section where the other variables are present, we need to add some additional ones that we'll use:

// The laser we will be shooting
public Transform laser;

// How far from the center of the ship should the laser be
public float laserDistance = .2f;

// How much time (in seconds) we should wait before 
// we can fire again
public   float   timeBetweenFires = .3f;

// If value is less than or equal 0, we can fire
private float timeTilNextFire = 0.0f;

// The buttons that we can use to shoot lasers
public List<KeyCode> shootButton;

One thing you may have noticed is that we have a laser variable that is of the type Transform. This is the laser we'll fire, which we will create shortly.

Inside our Update function, we will need to add some additional code, which is as follows:

// a foreach loop will go through each item inside of 
// shootButton and do whatever we placed in {}s using the 
// element variable to hold the item
foreach (KeyCode element in shootButton)
{
  if(Input.GetKey(element) && timeTilNextFire < 0)
  {
    timeTilNextFire = timeBetweenFires;
    ShootLaser();
    break;
  }
}

timeTilNextFire -= Time.deltaTime;

In a manner very similar to what we did before with the player movement, we check each of the keys we allow the player to shoot with (such as the spacebar and Enter keys). If they press any of these keys and can fire again, then we will reset our timer and shoot a laser. However, we haven't made the ShootLaser function. Let's do that now.

Underneath the functions, add the following function:

// Creates a laser and gives it an initial position in front 
// of the ship.    
void ShootLaser()
{
  // calculate the position right in front of the ship's
  // position lazerDistance units away
  float posX = this.transform.position.x + 
               (Mathf.Cos((transform.localEulerAngles.z - 90) * Mathf.Deg2Rad) * -laserDistance);
  float posY = this.transform.position.y + (Mathf.Sin((transform.localEulerAngles.z - 90) * Mathf.Deg2Rad) * -laserDistance);
  
  Instantiate(laser, new Vector3 (posX, posY, 0), this.transform.rotation);
}

Save your file, and go back into Unity. You'll now see a number of additional variables that we can now set. Be sure to set the Shoot Button variable in the same manner that we did the movement buttons, changing the Size to 2 and setting Element 0 to Mouse0 and Element 1 to Space.

Next, we will need to create our laser. Go back into our Assets folder from the example code, and move the laser.png file into our Project tab's Sprites folder.

Following that, drag-and-drop it into your scene from the Scene tab to place it in the level.

Right-click the Scripts folder you created earlier, click on Create, and select the C# Script label. Call this new script LaserBehaviour. Go into MonoDevelop, and use the following code:

using UnityEngine;
using System.Collections;

public class LaserBehaviour : MonoBehaviour 
{
  // How long the laser will live
  public float lifetime = 2.0f;

  // How fast will the laser move
  public float speed = 5.0f;


  // How much damage will this laser do if we hit an enemy
  public int damage = 1;

  // Use this for initialization
  void Start () 
  {
    // The game object that contains this component will be
    // destroyed after lifetime seconds have passed
    Destroy(gameObject, lifetime);
  }
  
  // Update is called once per frame
  void Update () 
  {
    transform.Translate(Vector3.up * Time.deltaTime * speed);
  }
}

Attach LaserBehaviour to the laser object. Finally, add a Box Collider component by first selecting the laser object and then going to Component | Physics 2D | Box Collider 2D. The collision box, by default, will be the size of the image, but I want to shrink it to fit what is visually seen of it. To do that, we will change the Size attribute's X property to .06 and Y to .5.

Now, the laser will move in the direction that it's facing and die after a period of 2 seconds! Next, let's make it so that the player can shoot them.

In the Project tab, go to the Assets | Prefabs folder, and drag-and-drop the laser object from our Hierarchy tab into it. You'll notice that the object Hierarchy will turn blue to show that it is a prefab.

Have a look at the following screenshot:

Now, delete the laser object from our scene, and then go to the playerShip object. Drag-and-drop the laser prefab into the Laser property of the PlayerBehavior component.

Finally, add a circle collider to our ship by going to Component | Physics 2D | Circle Collider 2D. Change the Radius property to .3.