Follow the next steps in order to register your website with Google and get the API keys:
1) Open your WordPress admin dashboard.
2) Navigate to the plugin settings page. There you'll see "Authentication" section.
3) Click "Get the API Keys" link to create the necessary keys.
4) You will be redirected to the following page https://www.google.com/recaptcha/admin#list. There you will see "Register a new site" block.
5) Choose the necessary reCAPTCHA version.
6) Enter your domain name.
7) Mark the "Accept the reCAPTCHA Terms of Service" checkbox and click "Register" button.
8) You will see "Adding reCAPTCHA to your site" block.
9) Here you have your Site key and Secret key. Copy them and paste to the appropriate fields on plugin settings page.
10) After that, click "Save Changes" button.
Then, you must test reCAPTCHA.
1) You will see "Test reCAPTCHA" button. Click on it.
2) Complete the reCAPTCHA to verify your keys.