Google Groups provides a convenient way for your users to send messages to groups of people they frequently contact. A group contains the email addresses of its members, so users can send a message to all the group's members using the single address for the group.
Users can use groups to more easily:
Communicate and collaborate with groups of people. For example, groups can be useful for departments, project teams, classes, office locations, special-interest groups, and more.
Manage access to your documents, sites, videos, and calendars. Users can share their content with groups instead of entering individual addresses. With a group, they can add or remove members once, and the changes are applied to all the Google documents, sites, videos, and calendars that they shared with that group.
As a Google Apps administrator, you can create and manage groups for your entire domain. With Google Apps for Business or Education, you can enable the Google Groups for Business service, which gives you the option to let users create their own groups. Learn more about Google Groups for Business
They can send email messages to a group, invite a group to a meeting, or share their Google documents, sites, videos, and calendars with a group.
A group can contain members who are inside your organization and, if you choose, outside your organization. If multiple domains are associated with your organization's Google Apps account, groups can contain members in any of your organization's domains. A group can also contain the addresses of other groups, so you can "nest" groups to create larger groups.