and When you first select Groups, you are told that you currently do not have any groups, and you can either Add New Members or List All Groups. SelectAdd New Members.

and You can either Search for an address to add or select List All which will bring up everyone in your address book. Unless you have a VERY large address book, choose List All.

Select the members of your address book that you want to include in your new address group by checking the check boxes next to their names.

In the Add to New Group field, choose an appropriate name for the group and select the Add button.

You will now see your list added to the Groups List, and it will be available when you choose Groups when under Compose.