Debit cards spend money you already have in a bank or credit union account, while credit cards borrow money you must repay later—often with interest or late fees if you do not pay on time. Per the U.S. Consumer Financial Protection Bureau, a main advantage of debit is staying within the cash you hold (unless your account allows overdrafts, which can add fees); a main advantage of credit is deferred payment, with the trade-off that unpaid balances can incur interest and fees. In short: debit helps avoid debt but can still overdraw; credit offers flexibility and borrowing power but can cost more if balances are carried.
Source: CFPB — How are prepaid cards, debit cards, and credit cards different?