New Economics Perspectives has the article Where Did the Federal Reserve Get All that Money? Economist Stephanie Kelton posted this in 2012 to publicize the remarks of Federal Reserve Board Chairman Ben Bernanke.
The Federal Reserve, like any bank, can acquire an asset simply by crediting a bank account. In other words, the bank pays by creating money. As Alan Greenspan explained, the Fed has an unlimited capacity to spend in US dollars. It can pay trillions of dollars with a single keystroke.
A friend just posted this on Facebook. Although it is 5 years old, it could stand to be reposted every day until enough people understand this.