What is the use of CVV No. printed on the backside of Credit Card .... ????
CVV numbers are NOT your card's secret PIN (Personal Identification Number).
You should never enter your PIN number when asked to provide your CVV. (PIN numbers allow you to use your credit or debit card at an ATM or when making an in-person purchase with your debit card or a cash advance with any credit card.)
CVV numbers are also known as CSC numbers ("Card Security Code"), as well as CVV2 numbers, which are the same as CVV numbers, except that they have been generated by a 2nd generation process that makes them harder to "guess".