help with recaptcha for registration

HI - i have added the recaptcha via custom fields to the registration form along with the the recaptha plugin. When configuring the recaptcha in the custom fields the site there is a place for 'Unique Key' (photo attached) . Google provides Site Key and Secret Key and I do not know what to put in the 1 field that is there - presuming both fields should be there to enter. We do have recaptcha setup on the site for other forms we use so we know it works.