Why when I press "RightArrow"the object do not go right?(only go forward),Why when I press "RightArrow" when the program start, the RES BOX does not move to right?

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class playerMovment : MonoBehaviour
{
public Rigidbody rb;

 public float ForwardForce = 2000f;
// Start is called before the first frame update
void Start()
{
   
    
    
}

// Update is called once per frame
//Fixed use when we use force or gravity something like that
void FixedUpdate()
{
    //To speed up
    rb.AddForce(0, 0, ForwardForce * Time.deltaTime);

    if (Input.GetKey(KeyCode.RightArrow)){
        rb.AddForce(500 * Time.deltaTime, 0, 0);
       // Debug.Log("right");
    }

    
    
    

       
}

}

Have you selected a Rigidbody in the inspector?