This is an additional check to ensure that your card is not being used by an unauthorised person.
For MasterCard and Visa, look on the back of the card for a 3-digit code on the signature strip. It will be either after the full customer account number or after the last 4 digits of the customer account number.
You’ll find your visa number at the top right of your visa. It is usually ten digits long and it is displayed in Arabic. You can use the chart here to translate your number.