You don't really have a degree in economics, do you?
And just how many of those with economic degrees predicted the current trouble?
New money is a stimulus to what? Inflation? That's the point of view of the Monetarians, and I think the Austrians.
Buying. When I get money, I buy things with it.
When the Fed buys securities from a primary dealer, the primary dealer has an incentive to buy things with it. Or lose interest on the cash.