A debit/check is a card (made by Visa, Mastercard, and others. Made avaliable to you mostly by banks) That acts very similiar like a credit card, but instead of borrowing money from those greedy bastards, money is automatically deducted right from your checking account instead when you make a purchase. Acts like a cash card.
You need a checking account and cash in your checking account to use a debit/check card. Checking accounts also have a monthly fee.
Visa and Mastercard debit cards can be used to purchase items online. They can also be used with ATM machines to get cash from your checking account.
Debit cards are what teenagers and college students use to pay for World of Warcraft subscriptions.