I'd love to more about how gift cards in general work. Is it like a numbered swiss bank account where when you buy a card and the account number/password under

I'd love to more about how gift cards in general work. Is it like a numbered swiss bank account where when you buy a card and the account number/password under the scratch-off on the back is your only access? Clearly there are multiple gift card networks, but how does a company go about getting a card setup for their brand/product? And how would a business like PIA be allowed to use other brand's cards? The idea of a gift card being a deposit would make sense in this case.