A burner card is a card that will be closed upon completion of the first transaction and cannot be used again. The merchant won’t have access to working payment information after your first transaction goes through, so you can sleep soundly at night.
The free service hooks to your bank account like any regular debit card but it generates a unique credit card number that is only good for the store you specify, and only good for exactly the amount you say. You can create a virtual credit cards that expire after just one use, so you will never get hit with a charge you don’t authorize.
This works great for subscriptions, free trials, and other times you need a credit card but don’t want to use your real one.