I think I got the gist of it. The government can "print money" and spend it however it pleases, but in doing so increases the amount in circulation which would .. I want to say devalue it but you've said it will decrease interest rates - I suppose they are related. To counter this it pulls money back out of the NG sector by trading bonds for currency, in order to keep interest rates at a desirable level.

Isn't this a temporary measure though? That money will go back into the economy once the bond is completed, leaving us back at square one but a few years down the track. Is the "out" here the money sink of tax which simply removes money from the economy completely, as you said?

Secondly, I think I need a bit more info on the environmental limiting factors; because as it reads now, it makes no sense to me why there are even debated budgets and concerns about how to fun infrastructure projects, if the government can afford anything it wants by just issuing more money. Obviously I'm likely taking the simplified explanation too far, when it seems that they have the means to create money and the tool (bonds) to control the backlash of excess.