While this is a very simple recipe, it's the first thing you must do before you can use any of the useful features in AWS Organizations.
The following is a high-level diagram showing the relationships between master accounts, members, and organizational units (OUs):
Organization units
We deliberately enable all the features of organizations. The consolidated billing option is available for backward compatibility; before Organizations, consolidated billing was your only option for linking accounts.
Do not use your master account for day-to-day tasks. Since it is so important, it doesn't make sense to risk using it and/or having access keys for it. If your master account somehow became compromised, it would impact all of your member accounts. Just don't do it.
The master account will always have a star next to its name.