What is there to understand? You have more money for the same resources, resources rise in price -  as simple as it gets, that's inflation.

You can call it money printing or quatitative easing, there is not that much of a difference, but just in case:

Quatitative tightening is removing money from circulation. Not notes necesarily, also the money that is just a book record in a company or a Bank. To achieve this you have several mechanisms but one of them is to sell bond. The CB sells bonds thus removing the money used to pay these from circulation.

You want to "ease", the you re-buy the bonds and money gets into circulation again.

This is the 6 year old version of it.