The media is perhaps responsible for this "print money" thing. It has been noted here that central banks do not actually "print" the currency you have. Each country has their own physical issuer of notes and coin. I think that it is the Treasury in America, which may contract the function out to a specialized outfit. Whatever, I dunno.
Central banks control (in theory, via a few methods) the money supply. Cash and coins are a very small fraction of the money supply, perhaps a single digit percentage of the total. Like anyone, I’d have to look it up (possibly on the Fed page somewhere I referenced previously, for America), and its included in what is known as the M1 part of the money supply.