User, Group, IP and Page selectors are tracker field types used in the trackers feature to link items to other objects or users. Sometimes these fields are automatically detected, such as a user selector detects the username of ther person creating the tracker item.
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.
In the tracker item view panel, the value of these fields will be displayed if the hidden/visible is checked for the user.
In the tracker item edit panel, a tracker administrator (perm tiki_p_admin_trackers) will see each field with the pre-selected right value and will be able to change them. A non administrator will not see them.