Buying is really a form of trading. In this particular case you trade "money" (in our day and time cash) for something else. To buy something you have to either want it or need it. And if you "want it" that means you want to keep it not use it. I.e. if you buy a painting you want to enjoy it, or if you buy a house you want to live it, etc. So that means this particular "item" is now (and at least for the time being) if "off the market". If you buy something because you need it, that means you either going to utilize or consume it. So you buy food to eat or you buy a knife to cut your fruits with. The latter option (utilization) means that that "item" is also "off market" for the time being. The former option (use) means that item is gone in its current form of matter. So in case of food you convert that to energy.
Historically "shinny metals" just appealed to the "cave man" some how. Gold is probably more than other because it does not erode or rust. And because of that appeal more of it became in demand to use for mostly cosmetics. You go to any museum of natural history and you see all kind of tools made out of iron, copper, bronze but not gold. You might see in more recent history some utensils made from silver and way less made of gold or painted with gold. The idea is, gold scarcity prevent it from being "production metal" and added to its cosmetic value, because everyone since the start of time is trying to keep up with Joneses. Think of Bitcoin today. Most people who trade it have no idea what it is and never "seen" one, but they "believe" they can get something for it or its price goes up and down and they might end making money from that "trade". And just like Bitcoin, gold most likely earned its status because people then were fascinated by it as much as they are today.
Fast forward few thousands years, gold indeed is unique. It is rare and not destructible. It also has some industrial applications; about 7% of the gold on the planet goes to that. Say you buy an ounce of gold today, what they heck are you going to do with it? You sure as heck are not going to eat it. You are not going to put it on your desk or the wall and watch it all day; it is pretty boring. So the only reason you would buy it is because you think in future time you will be able to sell it for much higher price. That means in the future you assume someone would need it or want it more than you do now. So it is pretty much a Ponzi.