The goal of QE is to increase the money supply and lower interest rates by injecting money into banks so that they can extend credit to businesses and consumers at a more attractive interest rate. This credit can enable businesses to expand, entrepreneurs to make their dreams a reality, and consumers to become homeowners. Once the economy has recovered, the Federal Reserve reverses the QE by selling the securities back into the market.
However, QE is only effective if the banks are willing to lend and potential borrowers are willing to take the risk, which isn't always guaranteed in a period of uncertainty. Another potential risk of QE is that lowering interest rates tend to increase inflation, which can increase the cost of living as businesses face higher raw material costs and pass them onto consumers.