I do not know about DA, but I can answer your second question.
When you register with PayPal, you have to provide them with your credit card details, which are then verified by them electronically. You will also have to select your billing currency, I selected US $ as IRS is not available. Once it is done your account is ready to use.
When you make a transaction with PayPal, the merchant payment gateway prompts you for your PayPal login and password, after which your are shown your shopping cart with the items you ordered. If everything in the list is ok, pay for it, and immediately your credit card is electronically swiped for the amount. It is reflected in your statement as PAYPAL *merchant's name*