What is a stock?
A stock (also called an equity or share) is a unit of ownership in a company. When a company wants to raise money to grow, it can divide itself into millions of small ownership slices and sell them to the public. Each slice is a share.
If a company issues 1,000,000 shares and you buy 1,000 of them, you own 0.1% of the company. That means you are entitled to 0.1% of any profits distributed as dividends, and if the company is ever sold, you get 0.1% of the proceeds.
Owning stock is fundamentally different from lending money (which is what bonds do). As a stockholder, you are an owner, not a creditor. That means higher potential upside — companies can grow enormously — but also higher risk. If the company fails, bondholders get paid first. Stockholders get whatever is left, which can be nothing.
How companies issue stock (IPOs)
When a private company wants to sell shares to the public for the first time, it goes through an Initial Public Offering (IPO). Investment banks help the company set an initial price, the shares are listed on a stock exchange, and they begin trading.
After the IPO, the company keeps running its business — the money raised goes to the company (or in some cases, early investors). From that point on, trading happens between investors on the secondary market. When you buy Apple stock today, you are buying from another investor, not from Apple directly. Apple already got its money.
Primary vs. secondary market
- Primary market: Company sells shares to the public → raises capital
- Secondary market: Investors trade shares with each other → company not involved
How exchanges work
Stock exchanges like the New York Stock Exchange (NYSE) and Nasdaq are the marketplaces where buyers and sellers find each other. Modern exchanges are almost entirely electronic — a system called a matching engine pairs buy orders with sell orders in fractions of a second.
Every listed stock has a unique ticker symbol — a short code like AAPL (Apple), MSFT (Microsoft), or TSLA (Tesla). When you place a buy order through your broker, it routes to the exchange and matches with someone willing to sell at that price.
US stock markets are open Monday–Friday, 9:30 a.m. to 4:00 p.m. Eastern Time. Some brokers also allow pre-market and after-hours trading, though with less liquidity and wider price spreads.
Why stock prices move
A stock's price at any moment is simply what a willing buyer will pay and a willing seller will accept. Prices rise and fall based on the collective judgment of millions of investors about what the company is worth — and that judgment is constantly being revised based on new information.
Earnings reports
A company beats or misses its quarterly profit forecast — often the single biggest driver of short-term price moves.
Future guidance
Management's outlook for the next quarter or year. Markets are forward-looking — they price in expectations, not just current results.
Interest rates
When rates rise, future earnings are worth less today (higher discount rate), and safe bonds become more attractive — both tend to push stock prices down.
Macroeconomic data
Unemployment, inflation (CPI), GDP growth — all affect expectations about corporate profits and Fed policy.
Sentiment and momentum
Fear and greed are real market forces. In the short term, stocks can move dramatically based on narrative, not fundamentals.
In the short term, sentiment and noise dominate. Over the long term, a stock's price tends to track the growth of the company's earnings. This is why patient investors who hold through volatility tend to do well: they let the fundamentals catch up.
How investors make money from stocks
There are two ways stocks generate returns:
Capital appreciation
You buy a share at $100 and sell it at $150 — that $50 gain is a capital gain. This is the primary source of return for growth stocks. You only realize the gain when you sell.
Dividends
Some companies distribute a portion of profits to shareholders as cash payments, usually quarterly. Dividend stocks provide regular income even if the share price does not move much. You receive dividends whether you sell your shares or not.
Total return = price appreciation + dividends reinvested. Historically, dividends have accounted for roughly 40% of the S&P 500's total return over the past century — making them far more important than most new investors realize.
Stocks vs. individual company risk
Owning individual stocks exposes you to two layers of risk:
Unsystematic (company-specific) risk
The CEO is arrested. A product fails. A lawsuit wipes out profits. This risk is unique to one company and can be diversified away by owning many companies.
Systematic (market) risk
A recession hits, interest rates spike, or a global crisis unfolds. All stocks fall together. This risk cannot be diversified away — it is the price of participating in markets.
The practical takeaway: for most investors, owning a broad index ETF (hundreds of companies) eliminates company-specific risk entirely while keeping exposure to the market's long-term growth. This is why Warren Buffett has famously recommended low-cost index funds for the vast majority of people.
The bottom line
A stock is a share of ownership in a real business. Over long periods, owning pieces of well-run businesses — through individual stocks or, more practically, diversified index funds — has been the most reliable way to grow wealth. The key is understanding what you own, keeping costs low, and staying invested through the inevitable volatility.
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Frequently asked questions
What exactly do I own when I buy a stock?+
You own a fractional share of the company itself — its assets, future earnings, and a vote at shareholder meetings. Owning one share of Apple doesn't mean you can walk into an Apple store and claim a MacBook, but it does mean you're a part-owner of one of the world's most profitable businesses and entitled to a proportional slice of any dividends it pays.
Why do stock prices go up and down?+
Stock prices move because of supply and demand on the exchange. Millions of buyers and sellers constantly reassess what a company is worth based on earnings reports, economic data, interest rates, news, and sentiment. When more people want to buy than sell, the price rises. When more want to sell than buy, it falls. In the short term, emotion drives a lot of this. Over the long term, prices tend to follow earnings.
Can I lose all my money in stocks?+
If you invest in a single company and that company goes bankrupt, yes — your shares could become worthless. This is the core argument for diversification: spreading your money across hundreds of companies so no single failure wipes you out. A broad index ETF like VTI holds over 3,600 US companies. For it to go to zero, the entire US economy would have to collapse.
What is the difference between a stock and a share?+
"Stock" usually refers to equity in a company in general (e.g. "I own Apple stock"). "Share" refers to a specific unit of that equity (e.g. "I own 10 shares of Apple"). In practice the terms are used interchangeably.
How do I actually buy a stock?+
You need a brokerage account — an account specifically for buying and selling investments. Open one online (Fidelity, Schwab, and Vanguard are well-regarded options), deposit money from your bank, search for the ticker symbol of the stock or ETF you want, and place a buy order. Most brokers charge $0 commission for stocks and ETFs.