How do I disable a module for the First Sidebar? I enabled the captcha when someone wants to post a comment, but it's also there when you try to connect to the site...

I don't know how to keep the module enable for the comments but not for the sign-in area.

Thank you for the help !!
On the Captcha configuration page (admin/config/people/captcha) you can set which forms should display a Captcha. 

By default, all user forms get a Captcha challenge. Set them to "No challenge", add the form ID of your comment form to the list and choose the challenge you want.