how do i fix unity cs8803

Hi lads Im new to coding,I was trying to make my first game,but it shows the error code CS8803:Top-level statements must precede namespace and type declarations How do I fix it?Heres my code btw

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

public class NewBehaviourScript : MonoBehaviour
{
    public float speed = 10f;

    Rigidbody rb;
}


    void Start()
    {
        rb = GetComponent<Rigidbody>();
    }

    void Update()
    {

        float xMove = Input.GetAxisRaw("Horizontal");
        float zMove = Input.GetAxisRaw("Vertical");
        rb.velocity = new Vector3(xMove, rb.velocity.y, zMove) * 10f;
    }

I tried many times

I was follow a tutorial online,I dont think I missed a step Thanks alot.