Money, to me, in its most basic broken down form, is an accumulation of societal value you have contributed, that you are able to redeem as favors from others.
(Forewarning: we are ignoring many economic variables below, for the sake of simplicity and ease of understanding)
Imagine if there was no currency.
Say you do your neighbor a solid. Let’s call it a favor. They can owe you one. You can redeem this favor at a future time when you need their help, as long as neither of you have forgotten about it. Now imagine they wrote you a note and signed it. This would be worth something to the two of you who agreed upon it.
Now imagine you specified exactly how much they should owe you. “Derek owes Alex 1 hour of manual labor or equivalent.” That’s a pretty specific and quantifiable favor. However, it only means something to the two of you. What if you need your roof cleaned, and Derek doesn’t know how to clean roofs?
Now imagine Ron owed Derek an hour of manual labor or equivalent, and Ron knew how to clean roofs. Would it not be nice if I could solicit help from Ron to clean my roof?
Hence, currency was born (let’s just pretend that is my understanding).
A note (or a bill) that states you have earned someone else helping you with X number of favors. The central police (aka the government) has mandated that all currency must be accepted within the governing body (the country in which they govern) no matter who issued it, as long as it is authentic.
Now what about currencies cross border?
(For simplicity, let’s pretend exchange rates are constant and do not fluctuate.)
If 20 USD = 20,000 KRW, does that mean the USD is better than KRW?
Well, 1 USD is certainly better than 1 KRW.
But 1 USD would be no better or worse than 1,000 KRW, both which could buy you the same soda.
1 Gallon = 3.785 Liters.
The Gallon is not better than the Liter. Yet they can both be used to quantify the same amount of volume or liquid.
I think this is a healthy way of thinking about it.