Sub accounts are only granted to users on MAX or higher accounts. They are a useful way of tracking bandwidth on the master account if you have many users / agencies on your account. Please note that there is no UI for sub users, as its entirely supported by the API. Contact the administrator of the plan that signed up with Encoding.com for more information. This feature is not automatically turned on by Encoding.com; you must request this by contacting the Help Desk. For full information on sub accounts, please check out the complete API documentation.
http://www.encoding.com/api/category/category/sub_account_api_documentation