Jumping error pelase help me fix it

Unity Engine
1

How can I make it so that I cant jump multiple times

using UnityEngine;
using System.Collections;
using static System.Runtime.CompilerServices.RuntimeHelpers;
using UnityEngine;

public class Jump : MonoBehaviour
{
[SerializeField] private float jumpHeight = 5f;
[SerializeField] private Rigidbody rb;

// Start is called before the first frame update
void Start()
{
rb = GetComponent();
}

// Update is called once per frame
void Update()
{

if (Input.GetKeyDown(KeyCode.Space))
{
rb.velocity = new Vector2(rb.velocity.x, jumpHeight);
}
}
}

2

Check whether your character is touching the ground. You can do this in a variety of ways, most straightforward is probably raycasting down from the character’s position. Then, disallow jumping if the character is not grounded.