There are three key concepts in book-keeping:

Customers and Suppliers, both of which can be either:	between Customers and Suppliers and always have:	Balance sheet and Profit & loss accounts, including:
Individuals/Sole traders Partnerships Limited Companies Clubs, Societies and Associations	a Date a Value a Type (e.g. cash sales, cheques, invoices)	Bank accounts Debtor & creditors accounts Capital & equity accounts Income & expenditure accounts
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The key to understanding how book-keeping works, and why software will give the results it does, is to understand these three concepts and the way they inter-relate.

The book-keeper's art and skill is recording exchanges of value - transactions - between people, companies, and organisations - entities - using accounts and the double-entry system.