MouseMovement

public class MouseMovement : MonoBehaviour
{

    public float mouseSensitivity = 100f;

    float xRotation = 0f;
    float YRotation = 0f;

    void Start()
    {
      //Locking the cursor to the middle of the screen and making it invisible
      Cursor.lockState = CursorLockMode.Locked;
    }

    void Update()
    {
       float mouseX = Input.GetAxis("Mouse X") * mouseSensitivity * Time.deltaTime;
       float mouseY = Input.GetAxis("Mouse Y") * mouseSensitivity * Time.deltaTime;

       //control rotation around x axis (Look up and down)
       xRotation -= mouseY;

       //we clamp the rotation so we cant Over-rotate (like in real life)
       xRotation = Mathf.Clamp(xRotation, -90f, 90f);

       //control rotation around y axis (Look up and down)
       YRotation += mouseX;

       //applying both rotations
       transform.localRotation = Quaternion.Euler(xRotation, YRotation, 0f);

    }
}