[firmgently]

Banks do it under fractional reserve banking.

"Lord Adair Turner, formerly the UK's chief financial regulator, said "Banks do not, as too many textbooks still suggest, take deposits of existing money from savers and lend it out to borrowers: they create credit and money ex nihilo* – extending a loan to the borrower and simultaneously crediting the borrower’s money account"." [0]

* hilarious use of Latin to make 'out of nothing' sound authoritative

[0] https://en.wikipedia.org/wiki/Fractional-reserve_banking