CharacterController doesn't rotate on my script...

I'm busy with making a fist person interface, but it doesn't work... I want to make a person that can walk, run, rotate, and - later on - shoot... I'm working with javaScript by the way... Here is my code:

 var turnSpeed : float = 5;
 var walkSpeed : float = 6.0;
 var runSpeed : float = 10.0;
 var jumpSpeed : float = 8.0;
 var gravity : float = 20.0;
 
 private var moveDirection : Vector3 = Vector3.zero;
 private var turnDirection : Vector3 = Vector3.zero;
 
 function Start () {
     //Screen.lockCursor = true;
 }
 
 function Update() {
 
     var controller : CharacterController = GetComponent(CharacterController);    
 
     if (controller.isGrounded) {
             moveDirection = transform.TransformDirection(Vector3(Input.GetAxis("Horizontal"), 0, Input.GetAxis("Vertical")));
             moveDirection = moveDirection * walkSpeed;
             
             turnDirection = transform.Rotate(Vector3(Input.GetAxis("Mouse X"), Input.GetAxis("Mouse Y"), 0));
             turnDirection = turnDirection * turnSpeed;
         }
         
         if (Input.GetButton ("Jump")) {
             moveDirection.y = jumpSpeed;
         }
     // Apply gravity
     moveDirection.y -= gravity * Time.deltaTime;
     
     // Move the controller
     controller.Move(moveDirection * Time.deltaTime);
     
     controller.Rotate(turnDirection * Time.deltaTime);
 }

The main problem is that there is an error on line 22 - I'm not sure, but the error says "Cannot convert 'void' to 'UnityEngine.Vector3". And if you can help me a little bit with the running script, that would be grateful...