Collision help needed

I am trying to make a jump system where you must be standing on an object too jump but I don’t know how to check the collision.

My code:

using UnityEngine;

public class PlayerJump2d : MonoBehaviour
{
    //Variables
    public float Height = 2;
    public Rigidbody2D rb;

    //Code

    void Update()
    {
        if(Input.GetKeyDown("space")  )
        {
          rb.AddForce(new Vector2(0f,Height),ForceMode2D.Impulse);
        }
    }
}

Just google “unity platformer tutorial” and learn the basics yourself. This is something that’s pretty simple. Nobody here will write the code for you.