Official accounts are associated to Organizations only and do not have to be associated to an organization but you cannot associate them to anything else.  Many sites refer to official accounts and billing as Class A billing.   

Before you can start to manage your accounts, it is a good idea to have a few things setup within your database.  First, you can create your billing cycles; this determines what time period to create the bill for, when CES generates the bill, due date, late payment date, etc.  Second, you can create account categories; this is an additional field to allow you to place each account into an additional category besides organization or site.