[Plugin: cbnet simple captcha] help

I installed the ‘cbnet reallysimple captcha’ plugin activated it and now it doesn’t show up on my comments form. I’m unsure if I’m supposed to adjust the theme code somehow. and if I am could someone please tell me how. I looked into the plug in API? And at the top is says Add Really Simple CAPTCHA to the comment form, using the comment_form_after_fields hook

I’m unsure of what that means or if it’s just part of the code and I don’t have to do anything.

My site is http://www.voiceofbaltimore.org please get back to me with some help.