File sharing

You have to turn on filesharing, it is off by default.

Those people are mistaken. Apple takes your privacy seriously. No sharing is enabled by default.

Once turned on, it gives access to the Public Folder on the drive. If you want to make more available, you need to specify exactly what else will be shared.

yes

After turning FileSharing on you can then choose what folder(s) to share, who to share them with, and what kind of access they have. So for example, you could add your Documents folder in the Shared Folder pane (the middle one) and then in the Users pane add who will be permitted to access that folder and whether they can read, write, or read and write to it. For any folder not specified, the user would have no rights at all. As Grant said, by default when you give file sharing rights to someone they'll have read & write access to your public folder but you can change that.