Most cards can be used everywhere Debit Mastercard is accepted. Simply provide your card to the attendant and they will be able to process the transaction just as you would with any other debit or credit card.
If you are using your card for an online transaction or making purchase over the phone, then you will need to provide the full card number, expiration date, and most likely the 3-digit CV code that is provided on the back of the card. Please note that most merchants will also verify your billing information. In particular, the ZIP code listed on your card account. If you received a "generic" card, and the card was not mailed to your place of residence, you may want to register the card for online access (see this article) and update the address listed on your account.
Your card can also be used in Apple Pay, Google Pay and Samsung Pay. For more information about using your card in mobile wallets please see this article.
Important Note: The sponsor organization that provided you with your card may have restricted use of the card at certain merchants, merchant categories or locations. You may want to contact the sponsor organization to determine if the have placed certain restrictions on your card. You can also contact customer service. For more information on merchant restrictions, please see this article.