Money is not valuable in itself — a banknote is just paper, and the digits in your bank account are just entries in a database. Money works because it solves a problem barter can't: the coincidence of wants. If you have shoes and want bread, pure barter requires finding a baker who happens to want shoes right now. Money is a universally accepted intermediary, so you sell shoes to anyone, then buy bread from anyone.
Economists define money by three jobs: a medium of exchange (everyone takes it), a unit of account (you price things in it), and a store of value (it holds worth over time). Modern money is fiat — backed not by gold but by collective trust and the government's authority. That trust is fragile: when people stop believing money will hold its value, you get hyperinflation, where prices double in days and cash becomes nearly worthless.
Between 2007 and 2009 Zimbabwe experienced one of the worst hyperinflations in recorded history. As the government printed money to cover its debts, trust in the currency collapsed and prices roughly doubled every 24 hours at the peak in November 2008 — an annual inflation rate estimated by economist Steve Hanke at around 89 sextillion percent. The central bank issued a one-hundred-trillion-dollar note that couldn't buy a loaf of bread. People abandoned the currency entirely, transacting in US dollars and South African rand, and eventually the government formally scrapped its own money. The paper hadn't physically changed — what evaporated was the collective belief that it stored value.