User groups allow different notifications to be sent to different groups of users. The various notification related pages list groups with check boxes to select groups. Here is where you define who is included in each of those groups. The currently defined list of groups is shown when you first click on the Groups tab under Users. Click on any group name to configure that group.

Configuration of a group simply consists of checking boxes to include users for any combination of each of the available notification types. If the user is missing a phone number, that option will be disabled. The entire group can be temporarily deactivated with the Disabled button. The notes area is for any arbitrary notes you wish to enter about this group.