How does the Fed get money As far as I'm aware, the Federal Reserve has 4.5$ Billion on its balance sheet.

Where did it get the money for buying all those assets?

I understand that it makes money out of interest on the bonds it holds, but where did it get the money to buy those bonds in the first place?
If you read Fed's balance sheet, you'll see a corresponding increase in its liabilities under various deposits. They simply credit the accounts of institutions who sold them the assets.