How do I make this jump function work?

Her everyone, I am in a course working with Unity, and we have been given a game that we need to modify. I will be as descriptive as possible and provide pictures. The game is very simple. The player spawns in a room with a countdown and has to shoot boxes. Some give points, some add time, some take away time. They player controller we are given can move around, but not jump. I have been trying to code in a jump mechanic to make a more platformer-styled game, but I really struggle when it comes to code because I am more of a 3D artist. I know this question probably gets asked a lot, but from looking at other people's issues I cannot seem to figure out how to relate what was told to them.

Here is a picture of what the game looks like as it is.

This is the code I am trying to work with. Note that even after adding a rigidbody component, nothing happens. I am not receiving any compiler errors, but the jump function is not working. Any ideas would be great help. Thank you!

 using UnityEngine;
 using System.Collections;
 
 public class Controller : MonoBehaviour {
     
     // public variables
     public float moveSpeed = 3.0f;
     public bool grounded = false;
     public float maxSlope = 60;
     public float jumpVelocity = 500;
     private Rigidbody rb;
 
     private CharacterController myController;
 
     // Use this for initialization
 
     void Awake (){
         rb = gameObject.GetComponent<Rigidbody> ();
     
     }
     void Start () {
         // store a reference to the CharacterController component on this gameObject
         // it is much more efficient to use GetComponent() once in Start and store
         // the result rather than continually use etComponent() in the Update function
         myController = gameObject.GetComponent<CharacterController>();
 
     }
     
     // Update is called once per frame
     void Update () {
         // Determine how much should move in the z-direction
         Vector3 movementZ = Input.GetAxis ("Vertical") * Vector3.forward * moveSpeed * Time.deltaTime;
 
         // Determine how much should move in the x-direction
         Vector3 movementX = Input.GetAxis ("Horizontal") * Vector3.right * moveSpeed * Time.deltaTime;
 
         // Convert combined Vector3 from local space to world space based on the position of the current gameobject (player)
         Vector3 movement = transform.TransformDirection (movementZ + movementX);
         
         // Apply gravity (so the object will fall if not grounded)
 
 
         //Debug.Log ("Movement Vector = " + movement);
 
         // Actually move the character controller in the movement direction
         myController.Move (movement);
 
         if (Input.GetKeyDown ("space") && grounded){
             rb.AddForce (0, jumpVelocity, 0);
 
         } 
 
     }
         void OnCollisionStay (Collision col)  {
             foreach (ContactPoint contact in col.contacts)   {
             
             if (Vector3.Angle (contact.normal, Vector3.up) < maxSlope)    {
 
             grounded = true;
                 }  
             }  
         
         } void OnCollisionExit(Collision col)  {
             grounded = false; 
         
         }


 
         
     }