Groups within Webmail are only for your personal use and each person must maintain their own. If you need to create a group for many people within a department, consider requesting a Mailing List from Doug Cox.
Open the Contacts Folder/Mailbox.
Select the New Group button.
Type a name for your Group List.
Use the
icon to search your Contact List or add contacts from the Campus Address Book.

Select which address book to use from the drop-down field next to Displaying. [My Domain] gives access to all members of the campus community. Contacts gives access to all entries within your personal contact list.
For each name you would like to add to the group, select the name and click the Add button or use ctrl+click to select multiple names at once and then click Add.
Add a description of your group to the Notes field for reference at a later date.
Click the Save button to finish and return to the Contacts folder or select the Save and New to continue entering new contacts.