Making text appear when a parameter is met.

[wfreeman480]

I am currently working on an rpg styled game and I have created a basic script. Essentially when a player is near an object and they press E then it activates the script. However as a newbie I haven’t worked with canvas and things like that. Could someone please give me some tips or advice on making a text appear above the object or maybe even a text box at the bottom of the players screen.
using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour
{
bool callActive = false;
 Vector3 playerPosition;
 Vector3 NPC;
// Vector3 position1 = new Vector3(0, 0, 0);
 //Vector3 position2 = new Vector3(0, 0, 0);
 float totalDistance;
 
 void Start() {

// playerPosition = gameObject.transform.position;

 }

 void Update() {
    playerPosition = gameObject.transform.position;
    NPC = GameObject.FindWithTag("Respawn").transform.position;
    distanceCalculator();
    callDistance();
 }

 public void distanceCalculator()
 {
     playerPosition = gameObject.transform.position;
     totalDistance = Vector3.Distance(playerPosition, NPC);
   
 }

 public void callDistance()
 {
     if(totalDistance<2 && Input.GetKey(KeyCode.E))
     {
         Debug.Log(totalDistance);
         callActive = true;
     }
     else if (totalDistance>2)
    {
        callActive = false;
    }
     if(callActive == true) 
     {
         Debug.Log("live");  
    }
    
 }
}

Also if you have any suggestions for my code in general please let me know.

[wfreeman480]

Update:
Here is my code. I have a text labeled “Text” under my canvas but the issue is I am getting a null reference. Not sure why or how that works.
using UnityEngine;
using System.Collections;
using UnityEngine.UI;
public class ExampleClass : MonoBehaviour
{

 public Text tex;
 bool callActive = false;
 Vector3 playerPosition;
 Vector3 NPC;
// Vector3 position1 = new Vector3(0, 0, 0);
 //Vector3 position2 = new Vector3(0, 0, 0);
 float totalDistance;
 
 void Start() 
 {
     tex.gameObject.SetActive(false);

 }

 void Update() {
    playerPosition = gameObject.transform.position;
    NPC = GameObject.FindWithTag("Respawn").transform.position;
    distanceCalculator();
    callDistance();
    isActive();

 }

 public void distanceCalculator()
 {
     
     playerPosition = gameObject.transform.position;
     totalDistance = Vector3.Distance(playerPosition, NPC);
   
 }

 public void callDistance()
 {
     if(totalDistance<2 && Input.GetKey(KeyCode.E))
     {
         tex.gameObject.SetActive(true);
         Debug.Log(totalDistance);
         callActive = true;
     }
    

    
 }

 public void isActive()
 {
     if(totalDistance>3)
     {
         callActive = false;
         tex.gameObject.SetActive(false);
     }
 }
}