Something that has the attributes of money is valuable because it has those attributes. Would-be barterers can use money to overcome the otherwise insuperable problem of discovering a Coincidence of wants.
Trade requires money. Let's examine this vital function of money with respect to the coincidence of wants:
My Chicken farm example:
You run a chicken farm, and you need to buy a great many things to keep your farm and family going.
In a given month you need - for instance - to buy chicken feed, to hire someone to repair your generator, to buy a nailgun to allow you to mend chicken barn #9, to hire a midwife to help give birth to your widowed daughter’s baby, to buy milk and bacon - and so on.
Some of these resources will be buyable with chickens or eggs.
And some of them will not - there's no coincidence of wants if the midwife or the nailgun owner don't want chicken meat or eggs. Because they can't replace their expendables with meat or eggs.
But all or most of these resources will be buyable with money - with Gold or Silver. Because offering money in a transaction vastly improves the chance of a coincidence of wants
My Chicken farm example - continued:
You’ve had a successful month at the farm, and you now have loads of chicken meat and/or eggs to sell.
100 people line up to buy what you’ve got.
* 50 of them have horribly devalued fiat money, food-stamps and a bad attitude
* 40 of them have plans for barter - some of which are better than others. One is willing to work on your farm for food: another is willing to sell you their body, another has a stack of AA duracell batteries, another has some miniature bottles of scotch - and so on, with dozens of variations. You have to gauge each transaction on its own merits - an exhausting process - and half of the barter offers are simply going to be unworkable.
* 10 of them have Gold and/or Silver.
Which customers will you prefer selling your produce to? They all want what you've got - but do you want what they've got? Again: real money vastly increases the chance of a coincidence of wants.
Only Gold and Silver fulfill all of the prerequisites of money. This gives them inherent value - useful (for instance) in a survival situation.
Of course Fiat currency can also be used to run a chicken farm. However in time all Fiat currencies - without exception - revert to their true value of zero. When our current Fiat currency is no longer trusted then only precious metals will act as money.
Hope this was helpful.
A small but important detail about chickens for the urbanites here. You do not need to buy feed for chickens! Chickens are natural grazers during the day, and seek high places to roost at night. The process repeats day after day, until the time comes to butcher. In this case, you snatch the chickens from the high places at night time (extremely poor night sight!). We did this for decades on the farm. The eggs can be found by simply looking for the nests. This same characteristic occurs for many similar wild fowl.
> “Which customers will you prefer selling your produce to?”
The one offering ammunition.