Via QE, the Federal Reserve conjured new "money" into existence (if we did this, its called forgery...not QE) & exchanged this new "money" to the largest banks for US Treasury bonds and financial assets (Mortgage backed securities). Banks were left flush with cash, the Fed holding $4.5 trillion in Treasury's and MBS. The suggested goal of this exercise was that QE would lower interest rates and this would settle the economic system and subsequently boost asset valuations.
How'd it work out? As far as asset prices, generally they have soared 300% to 400% but the part about lowering interest rates...not so much. The chart below shows the Federal Reserve holdings of over 5yr to 10yr US Treasury debt versus the yield on the 10yr Treasury. The Fed increased its holdings of 5 to 10yr US debt from $100 billion in early 2009 to nearly $900 billion by early 2013...and then lowered it back to just $290 billion currently. And the correlation on the 10 year yields...essentially zero.