Government prints money to buy back its bonds.
The result is prices rise as the country's currency is devalued.
In the US the first round of QE resulted in a 20% increase in food prices and a 59% increase in oil.
After QE2, food went up a further 15% and oil another 30%.
The general economy is not helped or boosted as a result of QE because essential consumer prices increase.
In fact, every $10 increase in the price of oil takes 0.3% off GDP.