Once upon a time, people landed on the shores of these here United States and bought Manhattan for a handful of baubles. Real estate prices have gone up since then.
On August 8, 1786 (more than 200 years ago—I point this out since you’re still on summer break and I’m sure your internal calculator isn’t working), the Continental Congress authorized the issuance of the US dollar. The term “dollar” had already been in use for some time thanks to Back to the Future Part 126 (which has yet to be filmed).
The US Mint was created by Congress in 1792. Unhappily for 40% of the people touring the building, the Mint doesn’t produce Girl Scout Cookies. Unhappily for the remaining 60% of the tourists who know what the Mint really does, they do not hand out samples.
Early money was chunky since it was made out of gold, silver, and the aforementioned beads. The first paper money was hand-drawn on cocktail napkins and people were therefore unsurprisingly skeptical. Unsurprisingly (again), War was the instigator of change (extra points for remembering the Greek Goddess of War).
The change (not to be confused with pocket change) came about because in 1861 Congress needed money to finance the Civil War. So they made it up and issued Demand Notes. Demand Notes were printed on orange paper with purple ink which is why they were nicknamed Greenbacks.
After a bunch of years, a bunch of dollars, and a bunch of wars, the Bretton Woods (which did not go to Dunsinane Hill – serious extra points for getting that one) Accord linked most currencies to the dollar. This system did not last forever. Bretton Woods also created the International Monetary Fund (IMF) which changed its name but pretty much has lasted forever.
Today, like the currency of most nations, the dollar is fiat money (not backed by any physical asset [and by “physical asset” economists generally mean gold]). You can use it to buy other kinds of cars besides Fiats.
More importantly, you can use money to buy things like food and shoes.
Banks are a good place to keep money, but that is a subject for another day.
Athena is the Goddess of War (but you knew that).
According to The Bard (by which I mean Shakespeare) Macbeth will be safe until Great Birnam Wood comes to Dunsinane Hill.