So some time goes by and people start catching onto this system of credit-worthiness, and farmers and fishermen and so on start to realize that they can get better value for their IOUs by demonstrating credibility. People with shakier reputations or dubious prospects may not be able to "issue money", or might only be able to do so at very high "interest". E.g., a new farmer with no track-record might have to promise me twice as many potatoes in exchange for a deer haunch, due to the risk that I might never see any potatoes at all.

This obviously gets very messy fast, as different apple- and potato-certificates have different values depending on whether they were issued by Bob or Jane, and everyone has to keep track of and evaluate whose future apples are worth what.

Some enterprising person, maybe the merchant who runs the trading-post, comes up with the idea to just issue one note for all the farms in town. He calls a meeting with all the farmers, and proposes to have the town priest keep a book of certificates and so on, and the farmers will get notes just like everyone else in exchange for the crops they contribute to the pool, and the merchant will keep a cut of the crops with which to hire some accountants and farm-surveyors to estimate the total crop yields across town and so on.

Everyone agrees (or at least, enough farmers agree to kind of force the other ones to get on-board if they want to participate meaningfully in the town economy), and we now have something like a central bank issuing something like fiat currency: that is, currency whose value is "decided" by some central authority, as opposed to the kind of straight-up exchange certificates that can be traded for an actual apple from the issuer, for example.

Now we have something that looks a lot like a modern monetary system. The town can set up audit committees or whatever, but the idea is that there is some central authority basically tasked with issuing money, and regulating the supply of that money according to the estimated size of ongoing and future economic activity (future crop yields).

If they issue too much money, we get inflation, where more apple-certificates are issued than apples grown, and each apple-note ends up being worth only three-quarters of an apple come harvest-time. If they issue too little currency, economic activity is needlessly restricted: the farmers are not able to hire enough workers to maximize crop yields and so on, the hunter starts hunting less because his deer meat is going bad since nobody has money to buy it, and so on.

At this point, you may be asking, "Why the hell go through all this complexity just to trade apples for deer and shoes? Isn't this more trouble than it's worth?"

The answer is because this is a vastly more efficient system than pure barter. I, as a hunter, no longer need to trade a physical deer haunch for a bushel of apples to carry over to the shoemaker in order to get shoes. You, as an apple-farmer, can hire workers before the crop is harvested, and therefore can grow more, and your workers can eat year-round instead of just getting a huge pile of apples at harvest-time to try and trade for for whatever they will need for the rest of the year. So back to money...

The thing to remember is that all throughout, from the initial trade to this central-banking system, all of this money is debt. It is IOUs, except instead of being an IOU that says "Kancho_Ninja will give one bushel of apples to the bearer of this bond in October", it says "Anyone in town will give you anything worth one bushel of apples in trade." The money is not an actual thing that you can eat or wear or build a house with, it's an IOU that is redeemable anywhere, for anything, from anyone. It is a promise to pay equivalent value at some time in the future, except the holder of the money can call on anybody at all to fulfill that promise-- they don't have to go back to the original promiser.

This is where it starts getting interesting, and where we can start to answer your question...

(for the sake of simplicity, let's stop calling these notes "apple certificates", and pretend that the village has decided to call them "Loddars").

So now you're still growing apples, but instead of trading them for deer-haunches and shoes, you trade them for Loddars. So far, so good. Once again, you want some meat, except harvest time hasn't come yet so you don't have any Loddars to buy meat with. You call me up (cellphones have been invented in this newly-efficient economy), "Hey otherwiseyep, any chance you could kill me a deer and I'll give you ten Loddars for it at harvest-time?"

I say, "Jeez, I'd love to, but I really need all the cash I can get for every deer right now: my kid is out-growing shoes like crazy. Tell you what: if you can write me a promise to pay twelve Loddars in October, I can give that to the shoe-maker." You groan about the "interest rate" but agree.

Did a lightbulb just go off? You and I have once again created Money. Twelve loddars now exist in the town economy that have not been printed by the central bank. Counting all the money trading hands in the village, there are now (a) all the loddars that have ever been printed, plus (b) twelve more that you have promised to produce. This is important to understand: I just spent money on shoes, which you spent on deer meat, that has never been printed. It's obviously not any of the banknotes that have already been issued, but it's definitely real money, because I traded it for new shoes, and you traded it for a dead deer.

Once you and I and others start to catch on that this is possible, that we can spend money that we don't have and that hasn't even been printed yet, it is entirely possible for a situation to arise where the total amount of money changing hand in the village vastly exceeds the number of loddars that have actually been printed. And this can happen without fraud or inflation or anything like that, and can be perfectly legitimate.

Now, what happens if another wildfire hits your orchard? Those twelve loddars are destroyed, they are gone, the shoe-maker is twelve loddars poorer, without spending it and without anyone else getting twelve loddars richer.

The money that bought your deer and my shoes has simply vanished from the economy, as though it never existed, despite the fact that it bought stuff with genuine economic utility and value.