Easy one mate.
If you've linked the account to ur Visa Debit card, and you make a payment, it will tell PayPal to hit ur card up for the total money you are paying, send the funds via PayPal to the Seller, and they receive an account balance in their PayPal account.
Sometimes a seller will not allow a payment without a payment from an account balance (meaning the money is there for sure), so we send a payment to a buddy (add a little extra for the inconvenience - just to be nice), and they send payment back resulting in a balance in ur PayPal account, which you then use to send to the seller.
Hope this helps.