Choose Address Book from the Tools menu. In the Address Book dialog box, go to File and choose New Group. In the new dialog box give the group a name and choose between three options on how you would like to add members to a group. You can choose members from your already stored address book by clicking on Select Members, or add a new contact to the address book by clicking on New Contact or by entering a Name and E-Mail and clicking on Add.
On the toolbar, go to Message and select New Message. Enter the desired group name in theTo box.