1. Introduction

In this tutorial, we'll learn how to implement two-factor authentication (2FA) on a WordPress site. Two-factor authentication is a security measure that requires users to provide two different types of identification before they can access their accounts. This significantly enhances the security of your WordPress site by making it difficult for unauthorized users to gain access.

By the end of this tutorial, you will be able to:
- Understand what two-factor authentication is and why it's important
- Implement two-factor authentication on your WordPress site

Prerequisites:
- Basic understanding of WordPress
- Administrative access to a WordPress site

2. Step-by-Step Guide

2.1 Install and Activate a 2FA Plugin

To add two-factor authentication to your site, we'll use a WordPress plugin. I'll be using the Two Factor plugin for this tutorial, but there are many other plugins available that offer similar functionality.

To install the plugin, navigate to your WordPress admin dashboard, then go to Plugins > Add New. Search for Two Factor, install it, and activate.

2.2 Configure the Plugin

Once the plugin is activated, go to Users > Your Profile. Scroll down and you will see the Two-Factor Options section. Here, you can select the methods you want to use for 2FA.

3. Code Examples

Unfortunately, WordPress doesn't allow direct code modification when it comes to plugins, as they are standalone applications. However, you can customize the plugin's behavior by using hooks and filters. Below is an example:

// This hook allows you to modify the allowed 2FA methods.
add_filter('two_factor_providers', function($providers){
    unset($providers['Two_Factor_Email']);
    return $providers;
});

The above code removes the Email method from the available 2FA methods.

4. Summary

In this tutorial, we have learned about two-factor authentication and how to implement it on a WordPress site using a plugin. We have also seen how to customize the behavior of the plugin using hooks and filters.

Next steps would be to explore other plugins and their configurations. You can also learn about implementing CAPTCHA in WordPress for added security.

Additional resources:
- WordPress Plugin Handbook
- Two Factor Plugin on WordPress.org

5. Practice Exercises

1. Install and configure a different 2FA plugin on your WordPress site.
2. Try to add a new two-factor provider by coding a custom plugin.
3. Research and implement a CAPTCHA system in addition to the 2FA.

Solutions and explanations are not provided as these exercises are open-ended and depend on the user's choice of plugins and their individual WordPress environment. Practice is key to mastering WordPress, so keep exploring and experimenting.