if you prefer to pay with your Visa/masterCard you may use "Płatności Allegro" (credit card or wire transfer), unfortunatelly not many sellers accept this form of payment (because they have to pay to Allegro about 3% of the transaction value, for the buyer, on the other hand, there are no extra fees).
But under "Formy płatności" you may see the link "Poproś o udostępnienie Płatności Allegro" (Ask [the buyer] for the possibility of Allegro Payment), I guess it sends your request via e-mail to the buyer, and if he agrees (I assume he would transfer on you those extra 3% fees), you could pay with credit card.
Of course your Allegro account must be fully activated:
Also you will receive a letter from Allegro in approx 10-14 working days with a code to put on your account ...
I'm afraid it's only if you asked for it.
The letter is sent by snail mail, I think, to the address you gave in your registration form, and its purpose is to confirm that you actually live where you claim to (in case you break the law and they need to track you down by the police).
However, the full activation is only an option, you may give them fake personal data and don't ask for the full activation of your account, as long as you pay for the things you buy, but in this case you can't use some features of the service (including Allegro Payments).