Sphere fly's when I want it to jump

Hey guys so I am trying to make a sphere jump. Also before you say anything I have only been using unity for 3 days… So I have this code but I can’t jump. I have searched for about 2 hours but couldn’t find anything to work. I have developed some apps in java but want to get into gaming. I have not learnt c# and I am basing everything off what I have learnt in java. Btw I could have used switch statements but do not want to use them. I had some code before which I was able to jump but it would only jump backwards

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

public class PlayerMovement : MonoBehaviour {
    public Rigidbody rbS;
    public float movementSpeed;
    private bool jump;


    // Time.deltaTime makes everything frame rate independent
   

    private void Start()
    {
        rbS = GetComponent<Rigidbody>(); 
    }
    void FixedUpdate () {
        if (Input.GetKey("a")) // This allows you to move left
        {
            rbS.AddForce(-movementSpeed * Time.deltaTime, 0, 0); // Adding a force on the x axis
        }
        else if (Input.GetKey("d")) // This allows you to move right
        {
            rbS.AddForce(movementSpeed * Time.deltaTime, 0, 0); // Adding a force on the x axis
        }
        else if (Input.GetKey(KeyCode.Space)) // This is supposed to make you jump
        {
            rbS.AddForce(0, movementSpeed * Time.deltaTime, 0);  // Adding a force on the y axis
        }
        else if (Input.GetKey("w")) // This is supposed to make you go forward
        {
            rbS.AddForce(0, 0, movementSpeed * Time.deltaTime); // Adding a force on the z axis
            
        }
       
        else if (Input.GetKey("s")) // This is supposed to make you go back
        {
            rbS.AddForce(0, 0, -movementSpeed * Time.deltaTime); // Adding a force on the z axis
        }

       
		
	}
    
}

Change Input.GetKey(KeyCode.Space) to Input.GetKeyDown(KeyCode.Space) so that it only adds the force once when you press the button, rather than adding force the entire time the space button is pressed. You probably also want to specify the ForceMode as Impulse, i.e. rbS.AddForce(0, forceValue, 0, ForceMode.Impulse);