We are donating twenty gift cards to a school raffle. Can I make them all at once?

One at a time, and it is about ten seconds each. On Marketing → Gift cards fill Amount in the Sell a gift card panel, add a Note such as school raffle so you can find them later, and press Issue the card. The page comes back with the code, you write it on a card, and you repeat. There is no button that makes twenty in one go today. Every card you make counts under Issued and, until it is spent, under Outstanding, which is money you owe even though you gave it away. If a card is never used, cancel it from its page and the balance is written off.