Followed this official tutorial, my own version on GitHub, and you can see it in action here (WSAD to move, mouse click to shoot).

Steps on how to create this:

1. Create a new 3D project
2. Save the scene as Main
3. Create -> 3D object -> Plane
4. Create -> 3D object -> Cube
   1. Add Component -> Physics -> Box collider
   2. Add Component -> Physics -> Rigidbody
   3. Drag and drop this object in the Assets/Prefabs folder
   4. Make duplicates (use snapping to move by using the ctrl key)
   5. Make a row of them (about 8) and then make a new empty object and drag them all into this object
   6. Now duplicate this object and position above (again by using snapping with ctrl key)
5. Create -> 3D object -> Sphere
   1. Add Component -> Physics -> Sphere collider
   2. Add Component -> Physics -> Rigidbody
   3. Make it into a prefab
   4. Delete it from Hierarchy
6. On the camera object => Add Component -> Script:

   1. #pragma strict
      
      public var projectile : Rigidbody;
      public var shotPos : Transform;
      public var shotForce : float = 1000f;
      public var moveSpeed : float = 10f;
      
      
      function Update ()
      {
          var h : float = Input.GetAxis("Horizontal") * Time.deltaTime * moveSpeed;
          var v : float = Input.GetAxis("Vertical") * Time.deltaTime * moveSpeed;
          
          transform.Translate(new Vector3(h, v, 0f));
          
          if(Input.GetButtonUp("Fire1"))
          {
              var shot : Rigidbody = Instantiate(projectile, shotPos.position, shotPos.rotation);
              shot.AddForce(shotPos.forward * shotForce);
          }
      }

   2. Drag the Sphere prefab to the projectile
7. Create empty game object and rename to shotPos
   1. drag and drop it on the camera
   2. reset transform origin
   3. Position y=-0.5, z=1
   4. Rotation x=-15
8. Drag Camera to shot pos variable in the script
9. If you want to clean up the bullets after 2 seconds, add script to Sphere prefab:

   function Start () {
   	Destroy(gameObject, 2f);
   }