The assignment of debits and credits follows the accounting equation. Assets are on the left side of the equation therefore the left or debit side is the normal balance for assets. Liabilities and equities are on the right side therefore the right or the credit side is the normal balance for liabilities and equity. Withdrawals, revenues, and expenses really are changes in owner's equity but it is necessary to set-up temporary accounts for each of these items to accumulate data for statements. Withdrawals and expense accounts represent decreases in owner's equity therefore they are assigned debit balances.
Revenue accounts represent increases in owner's equity therefore they are assigned credit balances.
Double-entry accounting is an accounting system that records the effects of transactions and other events in at least two accounts with equal debts and credits. The total amount debited must equal the total amount credited. Therefore, the sum of the debit account balances in the ledger must equal the sum of the credit account balances. The process of recording the transactions in a journal is called journalizing. A General Journal is the most flexible type of journal because it can be used to record any type of transaction.