My form can be sent without filling reCaptcha

I don't know, how to validate the »recaptcha-checkbox-checkmark«. My form can be sent without filling reCaptcha. I don't understand what is meant in chapter »Verifying the user's response« I'm not a programmer, Please help. -- You received this message because you are subscribed to the Google Groups "reCAPTCHA" group. To unsubscribe from this group and stop receiving emails from it, send an email to recaptcha+unsubscribe@googlegroups.com. To post to this group, send email to recaptcha@googlegroups.com. Visit this group at http://bit.ly/1dkFnYd. For more options, visit http://bit.ly/P65DvS.