BillingPlatform allows for you to create two different types of users. The two types of users are internal and external.
Application Users have access to all accounts and all nodes dictated by their role. These types of users tend to belong to your organization as opposed to external users.
External Users have access to their own accounts data. These types of accounts typically belong to clients, as they only need the ability to view/pay their own invoices, see their account data, and change certain types of information.
Accounts have certain attributes that are determine how to application behaves when users are logged in using their personal accounts. These attributes are defined in the account creation process. More details are available in the appropriate tutorials.
Languages - Each account can use it's own preference for languages limited only by the number of languages you have created in BillingPlatform. Follow the link for more information on creating languages.
Themes - Each account can be assigned it's own theme to change how the application looks. This will allow each user to choose their own look and feel. Follow the link for more information regarding the creation of themes.
Roles - Each account uses a role to determine what they are allowed to view/edit in the BillingPlatform application. This allows you to have multiple types of users, and allows you to make changes across spans of users by altering a role. Follow the link for more information on managing roles.