Many websites give you the option to log-in to Facebook or to create your log-in with a username and password.
It's best to avoid using Facebook to log into other services since that locks you in with an active Facebook account that is very difficult to undo later.
If you used Facebook to create other account logins with other services, you need to cancel those other accounts. Any activity will cause your Facebook account to remain active.
In mid April of 2018 Facebook will be adding the ability to see all the apps you have connected and provide an option to undo those connections.