Via the process of federal-reserve style banks, mostly. They are allowed to create money. They don't lend out money of the depositors. They create it out of thin air by the authority of the government who has allocated these banks a special position, thus making these banks unfathomably wealthy. Unbelievably corrupt.

It may be screwed up, but it seems to be the best system humanity has created to date.

The alternative of a mineral backed currency that can’t adjust with population levels and is inherently deflationary we know to be far worse.