memes

In a central banking system, the central bank can create and destroy money from nothing. All banks can do it, though banks that aren't the central bank need to hold on to a reserve portion which iirc is 10%, so they can loan out (effectively creating) 90% of deposits, which compounds (ie, if you deposit $100, the bank can lend out $90 of that, and if that borrower puts that $90 in their account, then the bank can loan another $81, meaning for the original deposit of $100, now $271 exists, and that $81 can be loaned against, too).

Congress can borrow money from the central bank or other banks. It's also possible that they could seize the central bank and then just say they have the money and use that, though that's how Germany ended up with stories of people using a wheelbarrow full of cash to buy a coffee or diners paying when they ordered because prices would have gone up by the time they finished eating.