Show picture when object is hit

I'm making a game in unity and it I want to make a picture/text show up when my character walks into a box. This is my code so far:

using System.Collections; using UnityEngine;

public class Winbox : MonoBehaviour { private void OnTriggerEnter(Collider other) { GameObject.Find ("FirstPerson").SendMessage ("Finnished"); } // Use this for initialization void Start () {

 }
 
 // Update is called once per frame
 void Update () {
     
 }

}

So now when I hit the box, a message is sent with the text finnished. But you can't see that on the gamescreen. Does anyone have an idea how I can do that?