To use reCAPTCHA, you should get a sitekey from Google and insert it into your /assets/js/script.js. Please open script.js to learn how you can get one.
Now, you can create a reCAPTCHA with
<div data-provide="recaptcha"></div> and set the settings using data attributes. See available data attributes. Also, learn how you can verify the user's response here or here.