Imcorn, forget about transfering money or adding funds. That was necessary in the past. Now, paypal doesn't need you to do it. You just need to enter in your credit card details in the payment section and pay for it. Paypal will verify your credit card, then proceed to withdraw from your credit card company. The amount in your paypal account will remain "$0" after the payment.
Just do it like what you would do for buying things from any other online shop that supports credit card payment.