With the stroke of a pen, or more accurately these days, the click of a mouse. It doesn't actually print anything. The amount of printed banknotes in circulation are only a couple of percent of the actual money supply.
They print the money and then give it to Obama so he can keep it in his stash and give it away when he wants.
[ame=http://www.youtube.com/watch?v=fOZ-Etb0k0Q]Obama Money - Where Did it Come From? - YouTube[/ame]