Stock market basics
What a share is, where stocks trade, and why costs usually matter more than stock picking.
Stock Market Basics
Three hundred dollars a month, put into a broad index fund and left alone for forty years at 7%, ends up near $787,000. Nothing in that sentence required you to find a winning stock, listen to an earnings call or guess what the Federal Reserve does next. The market pays you for owning a slice of business and for staying long enough to collect it.
What you are actually buying
A share is a legal claim on part of a company. Buy one and you own a fraction of its future profits, its factories, its patents and its mistakes. You do not get a vote that changes anything, and no company owes you a dividend.
Prices move for two reasons. The first is earnings: a company that earns more per share next year is worth more. The second is the multiple, the amount investors will pay for each dollar of those earnings. Earnings grow slowly and relentlessly. Multiples breathe, and in bad years they stop breathing.
Bear markets are conventionally declines of 20% or more from a high. Most have lasted about a year; bull runs have usually lasted several years. Both averages hide enormous variation. The S&P 500 fell 38.5% in calendar 2008 and 19.4% in 2022.
How a trade actually happens
You will never stand on an exchange floor. The New York Stock Exchange, which traces back to 1792, and the Nasdaq, the first fully electronic market in 1971, each list a few thousand companies, and a broker handles the route for you. Stock and ETF commissions at the large US brokers are $0. A generation ago a trade cost $30.
- 01You place an orderAt your broker, for a dollar amount or a number of shares
- 02The broker routes itTo whichever venue offers the best price
- 03It is matched with a sellerUsually within a fraction of a second
- 04The shares settleIn your account one business day later
For a buy-and-hold investor almost none of this matters. What matters is which fund you bought and how long you hold it.
US settlement moved to one business day (T+1) in May 2024.
The indices you will keep hearing about
| Index | What it holds | Why it gets quoted |
|---|---|---|
| S&P 500 | 500 large US companies, weighted by market value | The default benchmark for the US market |
| Dow Jones Industrial Average | 30 large companies, weighted by share price | Oldest and most quoted, least representative |
| Russell 2000 | 2,000 smaller US companies | The standard read on small companies |
| MSCI World | Around 1,400 companies in 23 developed countries | What most global funds track |
| FTSE All-World | Developed and emerging markets, more than 3,000 companies | The whole investable market in one fund |
Market capitalization is share price times shares outstanding, and it separates the giants from the rest.
| Tier | Market value | Examples |
|---|---|---|
| Mega-cap | Above $200 billion | Apple, Microsoft, Nvidia |
| Large-cap | $10 billion to $200 billion | Starbucks, Target |
| Mid-cap | $2 billion to $10 billion | Shake Shack, Crocs |
| Small-cap | $300 million to $2 billion | Most Russell 2000 members |
The indices differ in how they are built. The S&P 500 and the Russell 2000 weight companies by market value, so the largest company has the largest influence. The Dow weights its thirty members by share price, so a $500 stock moves it more than a $50 stock regardless of company size. That quirk is a century-old artifact, and it is why almost nobody uses the Dow to benchmark a portfolio.
Why the index beats picking stocks
- What you need to get right
- Better: Nothing, except staying in
- Which companies win, and when to sell
- A company goes to zero
- Better: A small slice of one holding
- Possibly a large part of your portfolio
- Catching the next big winner
- Better: Guaranteed, in proportion to its size
- Only if you picked it early and held on
- Annual cost
- Better: 0.03% to 0.20%
- Trading costs, taxes and your time
VerdictTo beat the index you have to own the rare huge winners and avoid the blowups, consistently. The index gets the average of all of them, including the winners nobody saw coming.
To have held the best stock of the last decade you needed to own Nvidia, which rose more than a hundredfold between 2015 and 2025, and hold it through several falls of more than 50%. You also needed to avoid the companies that went to zero. Almost nobody does both consistently, and the evidence is not close.
Dividends are the other half people forget. Historically they have made up a large share of the S&P 500's total return, often put at around a third to 40% over long periods, and a price chart leaves them out. An index fund collects both without a decision, which is worth more than it sounds: the decision is where most investors lose.
What the market costs you
The cost of owning the market is the one thing about it you can know in advance. An index ETF costs 0.03% to 0.20% a year. An actively managed US stock fund typically charges 0.7% to 1.2% and still trails the index more often than it beats it.
- 0.05% expense ratio
- 1.25% expense ratio
The expensive fund still grows. It just hands about $75,000 to the manager over thirty years.
Illustrative. $300 invested monthly at 7% before costs, the fee subtracted from the return, compounded monthly, no taxes.
The 7% is an assumption, and an optimistic one for any single country over a short window. The fee is not an assumption. It is deducted in flat years and good years alike, on a balance compounding is trying to grow. On $100,000 held thirty years at 8% before costs, the same 1.2-point gap is worth about $283,000.
Account type matters as much as fund choice. In a regular brokerage account, dividends are taxed in the year you receive them, and so are gains you realize. A 401(k) or IRA defers or removes those taxes, so fill the tax-advantaged accounts first. When you do hold funds in a taxable account, broad stock index funds suit it well, because they pay modest dividends and rarely distribute gains.
Getting from here to invested
Build the cash buffer
Three to six months of expenses in a high-yield savings account or money market fund. This is what stops you selling shares in a bad month.
Open an account
Your 401(k) or an IRA first, then a brokerage account at a large low-cost broker. Check fund costs before the design of the app.
Buy one broad fund
A total-market or S&P 500 index fund. Get the first contribution invested before you optimize anything.
Automate the purchase
Same day as payday, same amount, every month. A $100 automatic investment beats a $300 one you have to remember.
Raise the amount when your income rises
A raise is the cheapest moment to save more, because you have not yet adapted to the money.
Fees and behavior decide nearly the whole outcome, and both are in your control. Stock selection is not. That asymmetry is the whole argument for owning the index instead of trying to beat it.
One exception, stated plainly. If you carry a credit card balance at 22% APR, this article is not your next step. Paying it off earns a guaranteed 22%, which no stock portfolio can promise. Build the emergency fund, clear the expensive debt, then come back to the market with money you will not need for ten years.
56 more deep dives are in the Navigator library.
