Debit cards take money directly from a checking account whenever you make a purchase or pay a bill. In other words, the transaction is completed using funds you already have.
For example, your checking account has $3500 in it. On Tuesday, you purchase a new phone for $1100, removing that amount from your checking account. Your new balance is $2400.
Later that week, you purchase a TV for $2500. Unfortunately, your checking account is short $100, so the purchase declines.
Whenever your checking account balance runs low, it can be funded by bank transfers or check deposits.
Debit cards are a great way to control your spending and can help with managing debt because they do not rely on borrowed funds.