trying to use lists to pickup an object and put in inventory

I am very new to C# programming and Unity, and currently am trying to teach myself about GUI and lists. I understand how lists work very well, but I am struggling to figure out how to say them and use them in code; all the tutorials I find are rather esoteric and over my head.

What I want to do is very simple; when I walk over an object, I want an icon to appear in an inventory indicating it has been picked up--but I want to do this using lists. I am unsure whether I can use GUItextures or if I should make the GUI in code. If anyone can show me a script that can do this or point to a tutorial that explains how to do this, I would appreciate you sharing it.

This is the script I have so far for my pickupobjects: using UnityEngine; using System.Collections;

 public class CoinDestroy : MonoBehaviour {
     public AudioClip pickupSound;
     private Vector3 spawn;
 
     // Use this for initialization
     void Start () {
         spawn = transform.position;
     }
 
     void OnTriggerEnter(Collider other){
         AudioSource.PlayClipAtPoint(pickupSound, spawn);
         Destroy(gameObject);
     }
 
     // Update is called once per frame
     void Update () {
     
     }
 }