As always, documentation is an ever-evolving entity, so I've added an issue to our tracker to expand on available fields from each Social Network/configuration of profiles
Yes, the next step will be to go into the Community Builder > Field Manager section and add new fields there for each field you wish to import from Facebook. Which ones you add are really dependent on what profile information you'd like to gather from Facebook on your site. The currently available Facebook fields can be found listed at the top of the components/com_jfbconnect/libraries/profile/facebook.php (and likewise for other social networks).
The field types that JFBConnect currently supports for CB are text, textarea, editor textarea, date or webaddress. So add a new field with one of these types, set the name and title to something unique (title may be displayed to user, so something readable), and set the required/show at registration/published fields as desired.
After you add the field to CB, go back to the JFBConnect > Profiles area. You should see a longer list of CB fields now and can map them to the fields in the Facebook column.
Try that out and let me know if you have any further issues.
Thanks
-Melissa