1. First, enter the module settings page. Check "Use Captcha" option, select "Google reCAPTCHA" captcha type. After checking this option, Google reCAPTCHA feature will be enabled.
2. Fill Google reCAPTCHA Site Key. Please follow instructions to get one key and input it here.
You can refer to the link below to get the site key.
https://developers.google.com/recaptcha/intro
Please check the address below, where the key was generated.
http://www.google.com/recaptcha/admin