First, you need to have an API key, for this, go to https://www.google.com/recaptcha/admin. To gain access to this page, you’ll need to be logged into a Google account. You’ll be asked to register your website, so give it a suitable name, then list domains (for example tutsplus.com) where this particular reCAPTCHA will be used. Subdomains (such as webdesign.tutsplus.com and code.tutsplus.com) are automatically taken into account.
Once done, you’ll be given a site key and its partner secret key:
Copy and paste both site key and secret key by logging-in to your site under wp-admin / Wp Real Estate manager/ settings / api settings / Captcha and you are done with configurations.