On this tab, you can see a list of all members of the group. You can Edit () or Delete () users in the list. You can also Approve () members' requests for joining the group or Reject () them from the group. Once rejected, the user cannot request to join the group until they are approved again.
More resources can be found at Developer's Guide -> Modules -> Groups -> Overview.
Page url: http://devnet.kentico.com/docs/5_5r2/contexthelp/index.html?group_members_list.htm