最近在做的FPS剛好用到 順帶就解釋了下

using UnityEngine;
using System.Collections;

// MouseLook rotates the transform based on the mouse delta.
// To make an FPS style character:
// - Create a capsule.
// - Add the MouseLook script to the capsule.
//   -> Set the mouse look to use MouseX. (You want to only turn character but not tilt it)
// - Add FPSInput script to the capsule
//   -> A CharacterController component will be automatically added.
//
// - Create a camera. Make the camera a child of the capsule. Position in the head and reset the rotation.
// - Add a MouseLook script to the camera.
//   -> Set the mouse look to use MouseY. (You want the camera to tilt up and down like a head. The character already turns.)

[AddComponentMenu("Control Script/Mouse Look")]//設定指令碼路徑
public class MouseLook : MonoBehaviour
{
    public enum RotationAxes
    {                      //列舉座標軸
        MouseXAndY = 0,
        MouseX = 1,
        MouseY = 2
    }
    public RotationAxes axes = RotationAxes.MouseXAndY;      //定義X和Y軸 RotationAxes為旋轉軸

    public float sensitivityHor = 9.0f;// 水平靈敏度
    public float sensitivityVert = 9.0f;// 翻轉靈敏度

    public float minimumVert = -45.0f;//設定翻轉角度的最大值和最小值
    public float maximumVert = 45.0f;

    private float _rotationX = 0;//x軸旋轉角度

    void Start()
    {
        // 使剛體不改變旋轉
        Rigidbody body = GetComponent<Rigidbody>();
        if (body != null)
            body.freezeRotation = true;//凍結旋轉
    }

    void Update()
    {
        if (axes == RotationAxes.MouseX)//判斷旋轉軸是X or Y軸
        {
            transform.Rotate(0, Input.GetAxis("Mouse X") * sensitivityHor, 0);//圍繞X軸旋轉 乘以相應的靈敏度
        }
        else if (axes == RotationAxes.MouseY)
        {
            _rotationX -= Input.GetAxis("Mouse Y") * sensitivityVert;
            _rotationX = Mathf.Clamp(_rotationX, minimumVert, maximumVert);//Mathf.Clamp :限制value的值在min和max之間， 
            //如果value小於min，返回min。 如果value大於max，返回max，否則返回value

            transform.localEulerAngles = new Vector3(_rotationX, transform.localEulerAngles.y, 0);//localEulerAngles 自身尤拉角，
            //說這是物件自己相對於父物件的旋轉角度，該變數可用於讀取和設定該角度。不可以用於遞增，角度超過360度將會失效。
        }
        else
        {
            float rotationY = transform.localEulerAngles.y + Input.GetAxis("Mouse X") * sensitivityHor;

            _rotationX -= Input.GetAxis("Mouse Y") * sensitivityVert;
            _rotationX = Mathf.Clamp(_rotationX, minimumVert, maximumVert);

            transform.localEulerAngles = new Vector3(_rotationX, rotationY, 0);
        }
    }
}