Create a new Unity 2D project.

Save the current (empty) scene, naming it page1.

Add a UI Text object positioned at the top center of the scene, containing text Main Menu / (page 1) in a large font size.

Add a UI Button to the scene positioned in the middle center of the screen. In the Hierarchy panel, click on the show children triangle to display the UI Text child of this button GameObject. Select the Text button-child GameObject, and in the Inspector panel for the Text property of the Text (Script) component, enter the button text called goto page 2, as shown here:

Add the current scene to the build, choosing menu: File | Build Settings…. Then, click on the Add Current button so that the page1 scene becomes the first scene on the list of Scenes in the Build.

Create a C# script class, MenuActions, containing the following code, and add an instance as a scripted component to the Main Camera:

using UnityEngine;
using System.Collections;

public class MenuActions : MonoBehaviour {
  public void MENU_ACTION_GotoPage(string sceneName){
    Application.LoadLevel(sceneName);
  }
}

Ensure that the Button is selected in the Hierarchy and click on the plus sign "+" button at the bottom of the Button (Script) component, in the Inspector view, to create a new OnClick event handler for this button.

Drag the Main Camera from the Hierarchy over the Object slot—immediately below the menu saying Runtime Only. This means that when the Button receives an OnClick event, we can call a public method from a scripted object inside the Main Camera.

Now, select the MENU_ACTION_GotoPage() method from the MenuActions drop-down list (initially showing No Function). Type page2 (the name of the scene we want to be loaded when this button is clicked) in the text box, below the method's drop-down menu. This page2 string will be passed to the method when the button receives an OnClick event message, as shown here:

Save the current scene, create a new empty scene, and then save this new scene as page2.

Follow the similar steps for this scene. Add a UI Text GameObject, displaying the text Instructions / (page 2) in a large font size. Add a UI Button, showing the goto page 1 text.

Add the current scene to the build (so now, both page1 and page2 will be listed in the build).

Add an instance of MenuActions script class to the Main Camera.

Select the Button in the Hierarchy panel, and add an On Click event handler, which will pass the MENU_ACTION_GotoPage() method the string page1 (the name of the scene we want to be loaded when this button is clicked).

Save the scene.

When you run the page1 scene, you will be presented with your Main Menu text and a button, which when clicked, makes the game load the page2 scene. On scene page2, you'll have a button to take you back to page1.