Help changing input to axis

Hello guys I coded this movement some time ago, and, I need now to change my movement from the input to the axis. I haven't used axis, because the negative values need to rotate the character too. Can anybody help me changing the following code input to axis input? I really appreciate it, thanks anyway

         void Update() {
                 moveVector = Vector3.zero;
                 playerController = GetComponent<CharacterController> ();
                 //Directions
                 Vector3 yForward = Camera.main.transform.forward;
                 yForward.y = 0.0f;
                 Quaternion rotationForward = Quaternion.LookRotation (yForward);
 
                 Vector3 yRight = Camera.main.transform.right;
                 yRight.y = 0.0f;
                 Quaternion rotationRight = Quaternion.LookRotation (yRight);
 
                 Vector3 yLeft = Camera.main.transform.right * -1f;
                 yLeft.y = 0.0f;
                 Quaternion rotationLeft = Quaternion.LookRotation (yLeft);
 
                 Vector3 yBackward = Camera.main.transform.forward * -1f;
                 yBackward.y = 0.0f;
                 Quaternion rotationBackward = Quaternion.LookRotation (yBackward);
 
                 vSpeed -= gravity * Time.deltaTime;
                 Vector3 yDownward = Vector3.down;
                 yDownward.x = 0.0f;
                 yDownward.z = 0.0f;
 
 
                 //Movement
                 if (playerController.isGrounded){
                         moveSpeed = walkSpeed;
                         vSpeed = 0.0f;
                         if (inCombat == false) {
                                 if (Input.GetButton ("Forward")) { 
                                         transform.rotation = Quaternion.Lerp (transform.rotation, rotationForward, rotationSpeed * Time.deltaTime);
                                         Vector3 forward = transform.TransformDirection (Vector3.forward);
                                         moveVector += transform.forward;
 
 
                                 }
                         
                                 if (Input.GetButton ("Right")) {
                                         transform.rotation = Quaternion.Lerp (transform.rotation, rotationRight, rotationSpeed * Time.deltaTime);
                                         Vector3 forward = transform.TransformDirection (Vector3.forward);
                                         moveVector += transform.forward;
 
                                 }
                         
                                 if (Input.GetButton ("Left")) {
                                         transform.rotation = Quaternion.Lerp (transform.rotation, rotationLeft, rotationSpeed * Time.deltaTime);
                                         Vector3 forward = transform.TransformDirection (Vector3.forward);
                                         moveVector += transform.forward;
 
                                 }
                                 if (Input.GetButton ("Backward")) {
                                         transform.rotation = Quaternion.Lerp (transform.rotation, rotationBackward, rotationSpeed * Time.deltaTime);
                                         Vector3 forward = transform.TransformDirection (Vector3.forward);
                                         moveVector += transform.forward;
                                 }
 
                                 if (Input.GetButton ("Fire2")) {
                                         moveSpeed = runSpeed;
                                 }
 
                                 playerController.Move (moveVector.normalized * Time.deltaTime * moveSpeed);
 
                                 float playerSpeed = playerController.velocity.magnitude;
                                 anim.SetFloat ("Speed", playerSpeed);
 
 
 
 
                         }