Credit is borrowing money, debit is like an electronic check. With a credit card you have to pay the credit card company every month plus a small fee for borrowing their money, with a debit card every time you use it the money spent is just deducted right out of your bank account.
Ain't no accountant, but I use my debit card heavily. I don't make enough money to just be borrowing from people willy-nilly, I'll spend what I got and not spend what I don't got.
Oh, and "your credit" is like how trustworthy you are with loans. Having good credit means banks are more likely to give you larger loans at fairer interest rates. Some people use credit cards sparingly just to boost their credit, using them to purchase items like TV's and microwaves and pay them off right away. Stuff like that is good for your credit score I guess.
