dreamweaver site -re-captcha-server side & thank you page help needed

I have the captcha on my site but turns out it's not validating at all... I'm simply getting 130 spam a day....I put the codes for the key where they need to be but it's the "server side" part that doesn't say where to put the code etc... and how do I get it to go to my thank you page... my codes is below: my q's are 1):how do I get reCaptcha to do it's job/validate so they just click submit? 2)server side code - where does it go?

</script><script src='https://www.google.com/recaptcha/api.js'></script>

    <form method="POST" action="verify.php" enctype="multipart/form-data">
       <input type=hidden name="required" value="username,emailaddress">
       <input type=hidden name="missing_fields_redirect" value="http://www.XXXXXXXXXXXX.com/XXXXXXXXXXX.html">
       <input type="HIDDEN" name="recipient" size="-1" 
       <input type="HIDDEN" name="subject" value="Inquires from XXXXXXX XXXXXXXXX Website">
       <input type=hidden name="email" value="webforms@XXXXXXX.ca">
       <input type=hidden name="realname" value="Inquires form XXXXXX website">
       <input type="HIDDEN" name="redirect" size="-1" value="thankyou.html">
       <fieldset class="cf-fs1">
          <font face="Arial, Helvetica, sans-serif">
             <legend></legend>
             <br>
          </font>
          <font face="Arial, Helvetica, sans-serif"> 
          <label for="cf_field_2"><span><strong>Your Name: </strong></span></label>
          </font><strong><font face="Arial, Helvetica, sans-serif">
          <input name="username" type="text" id="username" size="30">
          <span class="reqtxt">(required)<br />
          <br />
          </span></font>
          </strong>
          <p><strong><font face="Arial, Helvetica, sans-serif"> 
             <label for="cf_field_3"><span>Phone Number:</span></label>
             <input name="phone" type="text" id="phone">
             <span class="reqtxt">(required)</span><br>
             <br>
             <label for="cf_field_4"><span>Email</span></label>
             : 
             <input name="emailaddress" type="text" id="emailaddress">
             <span class="emailreqtxt">(valid email required)</span><br>
             <br>
             <label for="cf_field_6"><span>Inquiry: </span></label>
             <textarea name="inquiry" id="inquiry"></textarea>
             </font><font face="Arial, Helvetica, sans-serif"></font></strong><font face="Arial, Helvetica, sans-serif"><br>
             </font> 
          </p>
       </fieldset>
       <fieldset class="cf_hidden">
          <legend>&nbsp;</legend>
          <div class="g-recaptcha" data-sitekey="XXXXXXXXXXXXXXXXXXXX"></div>
          <legend>
             <input type="submit" name="sendbutton" id="sendbutton" class="sendbutton" value="Submit" onClick="return cforms_validate('', true)"/>
             <br />
          </legend>
       </fieldset>
    </form>
    <br />