Easiest way is to connect it to your bank checking account. Or, If you Want to set it up with your new card, just go through the steps of creating an acct. Then, it will ask you to add a fund source, to which you then put in your card number.
It saves it for all transactions in the future, so you don't have to put your card in each time.
When you buy something, it automatically draws from your credit card, and into your paypal, and then to the merchant so the merchant never sees your card info.
If you have any not q's or I did a terrible job trying to explain, just ask away