When you enter records of money paid into and out of your bank account into the cash book, there is a delay of at least a couple of days until these transactions are cleared through the banking system and appear on your bank statement.
In a purchase ledger control account, the total outstanding invoices at the beginning of a period and invoices received during that period, less payments made for invoiced supplies, will give a balancing figure of invoices still outstanding at the end of the period - your creditors.
In a sales control account, the total of outstanding invoices at the beginning of the period and invoices raised during the period, less payments received for invoiced income, will give a balancing figure of invoices still outstanding at the end of the period - your debtors.
