What Is the Stock Market? How Equity Trading Actually Works

You tap “Buy” in a brokerage app and a few seconds later the order fills. What happened in those seconds? What is the thing you now own? And who set the price on your screen? Answer those three questions in order and you understand the stock market — which is what this article does.

What you bought: a small piece of a company

A share represents fractional ownership in a company. If a company has 1 million shares outstanding and you own 1,000 of them, you own 0.1% of the company. That’s not a metaphor; it’s a legal fact. As an owner you can vote on major company decisions at shareholder meetings, you’re entitled to dividends if the company distributes profits, and you hold a residual claim — if the company is ever sold, whatever remains after all debts are paid goes to the owners, in proportion to their shares.

These certificates of ownership are called shares or equity, and the stock market is where they change hands.

Where the hand-off happens: exchanges

An exchange is the marketplace where buyers and sellers meet to trade. Its core function fits in one sentence: provide a fair, orderly venue where prices get discovered and trades get executed. The two largest in the US:

Not every company can list. Exchanges have listing requirements — standards for revenue, shareholder count, and governance that a company must meet to get on the board.

Where the price on your screen came from

Nobody sets stock prices. Prices are determined by supply and demand — how many people want to buy versus sell at each price. When buyers outnumber sellers, they compete against each other and bid the price up until buying and selling interest balance. When sellers dominate, the competition runs the other way and the price falls to a new equilibrium.

So the question with actual content is: what makes buyers and sellers change their minds? News about the company itself (earnings, product launches, management changes), macroeconomic news (interest rates, inflation, GDP), market sentiment (fear, greed, momentum), and broader sector and market trends — all of it lands on one side of the scale or the other.

Who is on the other side of your trade

When you tap Buy, the other side isn’t “the market” as an abstraction. It’s one of a few specific kinds of participant.

Retail investors — people like you, trading their own accounts — are numerous but small relative to total volume. The bulk of volume belongs to institutional investors: mutual funds and ETFs pooling retail money, pension funds managing workers’ retirement savings, hedge funds running professional and often aggressive strategies, and insurance companies. In developed markets, institutions account for roughly 80–90% of trading volume.

Two other kinds of participant aren’t there to hold stock at all. Market makers (often bank-affiliated firms) quote a buy price and a sell price at all times, earn the bid-ask spread, and in doing so supply the market’s liquidity — when you want to trade, someone is there to take the other side. Arbitrageurs live off price differences between related securities, and their activity is what keeps the same thing priced the same across different markets.

Why prices move: four frameworks

Supply and demand explains the mechanism but not the motive — why does this group want to buy today and that group want to sell tomorrow? There are four main frameworks, and they aren’t mutually exclusive.

Fundamental analysis holds that a stock’s price should reflect the company’s true value — its ability to generate profits in the future. Analysts estimate that value from revenue, earnings, assets, and growth prospects; if the market price sits below the estimate, the stock is “cheap.” Technical analysis holds that price patterns and trends predict future moves: charts show historical prices and volume, and technicians look for shapes that repeat — head and shoulders, support, resistance. Market microstructure points the camera at the market’s own machinery: how order books, market maker behavior, and trading rules shape the prices that print. Behavioral finance says investor psychology drives prices — people are overconfident, make systematic errors, and follow each other (herding), producing patterns that rational models can’t explain.

Primary vs. secondary markets: who actually gets your money

Here’s the thing beginners most often get wrong: when you buy a stock, does the company get your money? Almost never. The primary market is where new shares are issued — when a company IPOs (Initial Public Offering), it sells shares to investors for the first time, and the money goes to the company. The secondary market is where existing shareholders trade with each other: every share you buy on the NYSE comes from another investor who is selling, and the company doesn’t see a cent of it. Everyday “trading stocks” happens almost entirely in the secondary market.

What “the market was up today” means

Individual stocks rise and fall on their own. When people talk about “the market” moving, they’re really quoting an index — a basket of stocks chosen to represent a market or a sector. The S&P 500 holds 500 large US companies, weighted by market cap, and serves as the default benchmark for “the US stock market.” The Dow Jones Industrial Average (DJIA) holds just 30 large companies, weighted by price, and is one of the oldest indexes in existence. The NASDAQ Composite covers every stock on the Nasdaq exchange, weighted by market cap. The Russell 2000 collects 2,000 small caps. When the news says “the market was up today,” it’s the S&P 500 nine times out of ten.

Back to the beginning: buying your first stock

The procedure itself is short:

1. Open a brokerage account — a firm that holds your stocks and executes your trades (Fidelity or Schwab, for example).
2. Fund the account: transfer money from your bank.
3. Place an order: tell your broker which stock to buy and at what price.
4. The order executes: it matches with a counterparty and completes.

Placing the order is where you meet your first real decision. A market order buys immediately at the best available price; a limit order buys only at your specified price or better. The first guarantees execution but not price, the second guarantees price but not execution — and that one trade-off is the doorway into the whole topic of order types.

References

• Bodie, Kane, Marcus, Investments, Ch. 1, 3. McGraw-Hill, 2020. ISBN: 978-1-26-057101-6.
• Malkiel, A Random Walk Down Wall Street. Norton, 2019. ISBN: 978-0-393-35192-2.