At the counter, pay by simply tapping your card on the POS terminal; wait for a few seconds: once the green light appears and the bip is heard, it means your transaction is confirmed. The printed receipt associated to your payment will be given by the merchant.
A contactless payment can be refused for an amount not exceeding USD 50 or equivalent, for safety reasons, and you might be asked to insert your VISA Debit card in the POS terminal to pay.