[dba-SQLServer] Setting permissions on databases

I have done all of my work on SQL Server on my own servers with only myself as a user.  I now have 
to set permissions to databases for other groups, at least I think they are groups.

At the client, SQL Server 2008.  I can see the permissions in the database properties in dialog for 
the databases.  One db that has three groups (although it says "Type" is user), but my newly created 
database only has one (my user).

I need to set my new database to give permissions to the same groups (or users) as the existing 
database has.  I try to right click on the box that displays users for the database / properties / 
permissions but there is no way to add it there.  Do I add new users / groups in Management Studio 
somewhere or do I have to go elsewhere?

TIA,

-- 
John W. Colby
www.ColbyConsulting.com