Create a new 2D project.

Add a UI Text GameObject to the scene with a Font size of 30 and placeholder text such as slider value here (this text will be replaced with the slider value when the scene starts).

In the Hierarchy panel, add a UI | Slider game object to the scene—choose the menu: GameObject | UI | Slider.

In the Inspector tab, modify settings for the Rect Transform to position the slider on the top-middle part of the screen and the text just below it.

In the Inspector tab, set the Min Value of the slider to 0, the Max Value to 20, and check the Whole Numbers checkbox, as shown here:

Create a C# script class called SliderValueToText, containing the following code, and add an instance as a scripted component to the GameObject called Text:

using UnityEngine;
using System.Collections;
using UnityEngine.UI;

public class SliderValueToText : MonoBehaviour {
  public Slider sliderUI;
  private Text textSliderValue;

  void Start (){
    textSliderValue = GetComponent<Text>();
    ShowSliderValue();
  }

  public void ShowSliderValue () {
    string sliderMessage = "Slider value = " + sliderUI.value;
    textSliderValue.text = sliderMessage;
  }
}

Ensure that the Text GameObject is selected in the Hierarchy. Then, in the Inspector view, drag the Slider GameObject into the public Slider UI variable slot for the Slider Value To Text (Script) scripted component, as shown here:

Ensure that the Slider GameObject is selected in the Hierarchy. Then, in the Inspector view, drag the Text GameObject into the public None (Object) slot for the Slider (Script) scripted component, in the section for On Value Changed (Single).

From the drop-down menu, select SliderValueToText and the ShowSliderValue() method, as shown in the following screenshot. This means that each time the slider is updated, the ShowSliderValue()method, in the scripted object, in GameObject Text will be executed.

When you run the scene, you will now see a slider. Below it, you will see a text message in the Slider value = <n> form.

Each time the slider is moved, the text value shown will be (almost) instantly updated. The values should range from 0 (the leftmost of the slider) to 20 (the rightmost of the slider).