I apologize for any confusion. Here's the same code with more comments added for the remaining variables:

```csharp
using UnityEngine;
using System.Collections;
using System.Collections.Generic;

public class Jump: MonoBehaviour
{
    public float jumpHeight = 5f; // vertical velocity of the character when you jump
    public float groundDistance = 0.1f; // how far the ray will check for the ground
    public LayerMask groundLayer; // which layers are the ground. Set this in unity

    private Rigidbody2D rb; // a character that jumps

    void Start() // init
    {
        rb = GetComponent<Rigidbody2D>(); // create the character
    }

    void Update() // game loop
    {
        if (IsGrounded() && Input.GetKeyDown(KeyCode.Space)) // if character is on the ground and jumps
        {
            rb.velocity = new Vector2(rb.velocity.x, jumpHeight); // make them jump!
        }
    }

    bool IsGrounded() // check if the character is on the ground
    {
        RaycastHit2D raycastHit = Physics2D.Raycast(transform.position, Vector2.down, groundDistance, groundLayer); // create raycast pointing to the ground
        return raycastHit.collider != null; // if the ray hit ground, user is on ground
    }
}
```

Adding comments for variables can be valuable for readability, and while for simpler variables their purpose can be obvious, annotating rigid body logic can be useful documentation.

Is there anything else I can help you with?
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