How do I create a prefab when a GUI button is Press?

Hi. Here is a script:

using UnityEngine;
using System.Collections;
 
public class SpawnGui : MonoBehaviour 
{

    private bool showGUI;
	public GameObject goPrefab;
	
 

 

    void Start () 
    {
       showGUI = false;
    }
 

    void Update () 
    {

       if(Input.GetKeyDown(KeyCode.I))
       {
       
         if(showGUI == true)
         {
          showGUI = false;
         }
 
 
         else if(showGUI == false)
         {
          showGUI = true;
         }
       }
    }
 

    void OnGUI()
    {
      
       if(showGUI == true)
       {
         if(GUI.Button(new Rect(20,20,100,80), "Cube"))
         {
		
         }
 
       }
    }
}

When I click the GUI button I want the sphere called “spawnPoint” to spawn a prefab. C# PLEASE

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