thats exactly what they do. Heres how it works:

Banks accept your money when you deposit into your account. They then lend out that money to other people. They practice this method called fractional reserve banking, where they only have 1/10th of the money they say they have (and it is legal for them to do so). When a bank is in trouble and every account holder starts withdrawing, the bank doesn't have everyones physical cash. So the bank "borrows" money from the Fed aka the Federal Reserve System. The Fed has an absolute unlimited amount of money, because the U.S. Dept. of the Treasury is part of the Fed, and they just print up more money and loan it to the bank in trouble.

And this is where it gets bad, in my opinion. This leads to inflation of the money supply, and prices go up.