How to Rotate gun while mouse moving? and How to fire bullet at mouse pointer ?

utube is banned in my country sry, so I couldn't see the video.

Is ur game First person controller? then it's pretty simple, the default one already has a Camera script, put in a script to fire the bullet.

 var bullet : Rigidbody;
 var throwForce : float;

 function Update () {
 
 if(Input.GetButtonUp("Fire1")){
     var cloneBullet : Rigidbody = Instantiate(Bullet, transform.position, transform.rotation);
     cloneBullet.name = "Bullet";
     cloneBullet.rigidbody.velocity = transform.TransformDirection(Vector3(0,0, throwForce));   
 }

Attach this to ur gun... then set the bullet rigidbody and throwForce(speed of bullet) in the inspector. For that targeting thingy (the cross in a circle) make a GUI texture if u want.

If ur game is Third person controller, u'll have to attach a camera script to it to make it rotate properly.

BTW u have to attach the gun with the camera, and make the throw force local among the gun to make it shoot the right way (in TPC)

...

Your Script Has a problem. Here is the right one: var bullet : Rigidbody; var throwForce : float;

 function Update () {
  
 if(Input.GetButtonUp("Fire1")){
     var cloneBullet : Rigidbody = Instantiate(Bullet, transform.position, transform.rotation);
     cloneBullet.name = "Bullet";
     cloneBullet.rigidbody.velocity = transform.TransformDirection(Vector3(0,0, throwForce));   
 }
 }