The way the central bank does this is by buying assets - usually government bonds .
The institutions selling those bonds (either commercial banks or other financial businesses such as insurance companies) will then have "new" money in their accounts, which then boosts the money supply.
central banks try to raise the amount of lending and activity in the economy indirectly, by cutting interest rates.
Lower interest rates encourage people to spend, not save. But when interest rates can go no lower, a central bank's only option is to pump money into the economy directly. That is quantitative easing (QE).
I think it is a bond purchasing concept inUS so that their economic condition becomes well and employment increases,
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A central bank implements quantitative easing by buying specified amounts of long term financial assets from commercial banks and other private institutions, thus increasing the monetary base and lowering the yield on those financial assets.
This is distinguished from the more usual policy of buying or selling government bonds in order to keep interbank interest rates at a specified target value.
See this wiki link http://en.wikipedia.org/wiki/Quantitative_easing