User, Group, IP selectors are tracker field types used in the trackers feature to attribute items to specific users. Adding a name to a tracker item is necessary but not sufficient to create special viewing and editing privileges - often used with User Tracker, registration tracker or Group tracker
The page Adding fields to a Tracker explains how the fields, (columns or questions) of a tracker are set up.
The automatic feeding option of the field type works exactly like the User Selector except that instead of the user name, it uses the IP of the user.