In short: a debit card is a payment instrument linked to your account, with which you pay and withdraw using your own money that is already in the account.
Simply put: Unlike a credit card, a debit card is not a loan — you spend what you have. It has an annual or monthly fee and some withdrawal fees. Limits and notifications help you spot someone else's payment in time.
Example: You have €300 in the account and pay €45 in a shop. €255 is left. If the account has an overdraft, you can pay more — but that is already credit.
Watch out: if the card is lost or stolen, block it at once — the sooner, the smaller the loss.
In the EU, the interchange fee between banks on debit card payments is capped at 0.2% of the amount (Regulation (EU) 2015/751, Article 3), and the merchant may not charge you a surcharge for paying with such a card (Directive (EU) 2015/2366, Article 62(4)).
Example: Bulgaria — the same EU rules apply; the card's own fees are in your bank's price list.
Check in your country — your bank's price list and whether surcharges are banned for other cards too.
Source: Regulation (EU) 2015/751, Article 2: https://eur-lex.europa.eu/eli/reg/2015/751/oj