Usually the top-level of an organization is represented by an account like this, whose components will be the inventory journal, accounts payable journal, accounts receivable journal, payroll, bank account, and so on. You define the fields of each transaction and the type of each fields. Some fields are multivalue. For example, an invoice can have a list of items on it, and each item has an inventory ID, a price, and a quantity. You define the attributes of each account.
Some attributes are simply totals of a particular field of the transactions posted to that account.
Others are arithmetic functions of other attributes. A composite account can define an attribute to be a function of the attributes of its component accounts, but an atomic account can only define new attributes in terms of its own attributes. You define how an account handles transactions that are posted to it. In fact, most accounts have only one way of handling transactions, so there is nothing to define. An atomic account handles transactions by putting them on its list of transactions in order of their date.