Error on running animating movement code,Question on animation movement

https://www.youtube.com/watch?v=whzomFgjT50&list=PLlay-Dk_UDFYjPk5p6fNhVpQo3JXWQTNV∈dex=3&t=667s This I where I copied movement code, It took a while to copy it all down, and after I followed everything it said to... I got this

UnassignedReferenceException: The variable animator of PlayerMovement has not been assigned. You probably need to assign the animator variable of the PlayerMovement script in the inspector. UnityEngine.Animator.SetFloat (System.String name, System.Single value) (at :0) PlayerMovement.Update () (at Assets/PlayerMovement.cs:18)

Heres my code using System.Collections; using System.Collections.Generic; using UnityEngine;

public class PlayerMovement : MonoBehaviour { public float moveSpeed = 5f; public Rigidbody2D rb; public Animator animator; Vector2 movement;

 // Update is called once per frame
 void Update()
 {
     movement.x = Input.GetAxisRaw("Horizontal");
     movement.y = Input.GetAxisRaw("Vertical");

     animator.SetFloat("Horizontal", movement.x);
     animator.SetFloat("Vertical", movement.y);
     animator.SetFloat("Speed", movement.magnitude);
     animator.SetFloat("Speed", movement.magnitude);
 }

 void FixedUpdate()
 {
     rb.MovePosition(rb.position + movement * moveSpeed * Time.fixedDeltaTime);
 }

}

I believe I did it all correctly, what did I do wrong? Need it for a High school project would greatly appreciate it