The Facebook addon for Hidden CMS allows you to:
1. Click on Addons then Facebook from the top menu.
2. Click Login with Facebook and you'll be redirected to the Facebook authorisation window.
3. Click Allow on the Facebook authorisation window, to let Hidden CMS send posts (see below)
4. You will then be redirected to the Facebook plugin in Hidden CMS, which should look like this:
To disconnect your Facebook account from the CMS, you need to go to Facebook itself.
Once you're logged in to Facebook, find the Applications page in your account settings and remove the one that's shown for your website or Hidden CMS.