Don't understand how i can rotate camera around player

I am trying to add another script to the player in the shooter survival tutorial so that when i hold down the middle mouse button it allows me to rotate the camera by dragging it This is my current code but to be honest I don't really know what I am doing. I have been trying to take parts from a tutorial by someone called Naman Jain on youtube but it is not really teaching me anything

 using UnityEngine;
 using System.Collections;
 
 namespace CompleteProject
 {
     public class CameraFollow : MonoBehaviour
     {
         public Transform target;            // The position that that camera will be following.
         public float smoothing = 5f;        // The speed with which the camera will be following.
         public float radius = 10;
         public float height = 10;
         public float angle = 0;
         public float rotationalSpeed = 100;
         public float horizontalSpeed = 2.0F;
         public float verticalSpeed = 2.0F;
 
         Vector3 offset;                     // The initial offset from the target.
 
 
         void Start ()
         {
             // Calculate the initial offset.
             offset = transform.position - target.position;
         }
 
 
         void FixedUpdate ()
         {
             // Create a postion the camera is aiming for based on the offset from the target.
             Vector3 targetCamPos = target.position + offset;
 
             // Smoothly interpolate between the camera's current position and it's target position.
             transform.position = Vector3.Lerp (transform.position, targetCamPos, smoothing * Time.deltaTime);
 
             transform.LookAt (target.position);
             float cameraX = target.position.x + (radius + Mathf.Cos(angle));
             float cameraY = target.position.y + height;
             float cameraZ = target.position.z + (radius + Mathf.Sin(angle));
 
             transform.position = new Vector3 (cameraX, cameraY, cameraZ);
 
             if (Input.GetMouseButton (2)) 
             {
                 float h = horizontalSpeed * Input.GetAxis("Mouse X");
                 float v = verticalSpeed * Input.GetAxis("Mouse Y");
                 transform.Rotate(v, h, 0);
             }
         }
     }
 }