The "stock market" is real. When you buy a share of stock, you give money (through your broker) to a real human being who previously owned that stock. That share of stock means you own an infinitesimal piece of a company. That's a real thing. When you sell that stock, you sell it to another real human being and they (through their broker) give you money for it.
Most of the rest of it is maddenly complicated and often seems completely disconnected from reality. Companies release good quarterly earnings and the stock drops. Companies whose economic prospects are rosy all drop in value because macroeconomic forces completely unrelated to their industries are bad, despite no effect on earnings. TSLA is a thing that consistently loses money but their stock is ~$400-500/share, for some reason...
And then we try to act like the DJIA is a good proxy for the economy, when the DJIA merely comprises the aggregate value of stock prices for just *30* companies.
And that's before we get into "animal spirits" or technical investing--which as far as I can tell is reading a "chart" with absolutely no knowledge of the actual underlying business a company is in.
So... I get that we consider much of it basically imaginary, because it's just buying/selling infinitesimal pieces of companies, often based on rational analysis but often also based on essentially following the trends up and down.
But it's only "imaginary" because we've given it this place of reverence and esteem which exceeds what it is--a place where, based on whatever reason/strategy you choose, you can buy "shares" of ownership in corporations and keep or sell them as you see fit.