How does EFT OPS work?

Assuming you mean EFTPOS (Electronic Funds Transfer Point Of Sale)... The customer uses either a credit or debit card to pay for goods. The card is 'read' by the cashier's register, and an electronic 'request' is sent to the customer's bank. If the funds are available (or the card has enough credit) - the funds are transferred from the customer's account to the store's account.