Today, my first blog about fiat money and something about credit money and credit instrument.

Fiat money has not only no particular value in use, it doesn't even really have a value in exchange except that which is decreed that it would have.
So fiat money is money which is intrinsically worthless. And its value exists by virtue of the fact that it is generally acceptable.
And fiat money, needless to say, is one of the most mysterious inventions of the human mind, and no economist has managed to explain exactly why it is that people will generally accept something as valuable when it clearly has no value other than that  which it is decreed to have.

A credit instrument is an obligation. And it's used as money because it has value. And the value that it has, of course, is a value which is based upon its credit-worthiness, in other words, how much credit or how much credence people give to the promise which is actually written down. What I'm receiving or using as an instrument for money purposes is somebody else's obligation.
Their preparedness to do something for me which might be to give me fiat money. That could be the promise which is incorporated in the cheque or the bill of exchange.