Can't get Really Simple Captcha to work in Salesforce contact form

Hi,
I would appreciate any help out there. Please keep in mind I know the very minimum about coding, html, php.
On our website, we originally had Contact Form 7 and Really Simple Captcha. But then we put in a Salesforce generated contact form (web to lead); well, actually the web designers put it in for us and as they are quite $$ I was hoping that I could get the Captcha option to work without having to go through them. Plus, I need to learn how to do it.
Please let me know if you need anymore info. So, basically right now the html is in the basic format from Salesforce.
Here’s the last part:

<label for=”description”>Message</label>
<textarea class=”wpcf7-form-control” name=”description”></textarea>

<input type=”submit” name=”submit” />

https://www.ads-software.com/extend/plugins/really-simple-captcha/