If you are using the TurboTax online editions and need to pay for the account, the payment information is in the File section of the program in Step 1. You select to Pay with a credit card. The following screen has all the fields to enter your payment information along with the credit card number, expiration date and the CVV number. The CVV number is entered in the Red box labeled Security Code
If you do not see this screen after selecting to Pay with credit card, then change your web browser.