Alfresco users and groups are created by the Alfresco administrator using the Alfresco Share Admin Tools. You can then assign these users and groups to Records Management roles using the Users and Groups tool in the Records Management Console.
Once you've assigned them to a role they'll be able to use the level of Records Management functionality that role has been given.
Note: There are some system groups that are generated by default, such as site_swsdp_SiteManager. These can't be assigned to a role.