Register on reCAPTCHA admin console to get your site and secret keys.
By default CAPTCHA challenge is triggered on form submit (i.e. when user clicks submit button). This is recommended but may be incompatible with some extensions. Version 1.2.0 added Trigger Method option to allow automatically triggering CAPTCHA on page load. If you're receiving Captcha answer is missing errors, enabling this option may solve the issue. CAPTCHA challenges triggered on page load are automatically refreshed every 2 minutes.