Customized groups are selections you have saved for future use. To save a selection - press the button "Save Selection" near the Addressee box. The Save Selection dialog will appear. You have two choices: create a new group or select one of the existing groups. In the latter case, your selection will be added to previously saved selection. All duplication of computer names will be removed. The saved selection will be shown in the List of computers under the Customized Groups title.