^ as I understand it, the purpose is to increase the proportion of money in the overall economy to encourage spending in the same way as just “printing money” in the Zimbabwe or Weimar Republic sense, but instead of doing it to just pay the government’s bills, the buying of the govt bonds serves as a vehicle to encourage those who are getting the cash to reinvest it in less safe places, helping to kickstart the economy via private institutions.
Realistically, both will likely cause inflation to increase as you’re changing the balance of money -> resources (tangible or intangible) in the economy, but QE attempts to get around the long term impacts of devaluation via the promise of carefully reversing the process once the economy has recovered (selling the bonds back to the market eventually), theoretically making the markets less nervous about inflation and hopefully holding prices back a little more than simply money printing would do.
Whether this holds in truth is… well… 
