A physical debit card looks and functions like other plastic credit cards. Many are associated with Master Card or Visa and bear the MC or VISA logo on the card. The debit card can be used anywhere the MC/VISA logo appears. Other cards are issued by banks or financial institutions and their cards can also be used like regular credit cards. Some are not plastic; they are designed to use over the phone or on the Internet.
The major difference and advantage to using a debit card is that there is no bill to pay later and no interest charges. Charges are paid or pending payment from the bank account immediately. If there is not enough money in the account, most attempts to charge will be refused unless there is some overdraft protection.
A debit card program may offer rewards or perks based on use. They offer the convenience of credit cards without the bills or interest charges. Some may add on a small fee for items like cash advances but there is no annual fee. A PIN number is used for debit card ATM advances. The use has the option to tell merchants to run the debit card as "credit" so payment is withdrawn slightly later instead of instantly.