Once the package has been installed, to activate reCAPTCHA you have to:

1. Login to your site as an administrator.
    
2. Find the "Captcha setup" page in your dashboard (it's located under System & Settings - Permissions & Access).
    
3. Choose the reCAPTCHA in the Active Captcha field.
    
4. The first time you need to obtain the reCAPTCHA keys. The procedure to do that is described in the "Captcha setup" page.