To create a new "User Group":

• Login using an account that has 'Administrator' privileges.
• Click Settings on the top-right, and select Manage Users from the menu.
• In the resulting page, click  Create User Group link under "Manage User Groups" section.
• In the page that appears, define desired settings. Then click "Save" button.

Once you create a user group - you can assign it to one or more users as explained here.