How Markets Work: Exchanges, Orders and Indexes

The first time you place a trade, the screen is full of unfamiliar words: bid, ask, limit, stop, volume, the index is up, the index is down. None of it is hard, but a few of these details decide whether you pay a fair price, and misunderstanding them is one of the most common ways beginners lose money on day one. This chapter explains where trades happen, the order types and what each risks, how to read a quote, what the indexes in the news actually measure, and which market signals to ignore.

Where trades happen

Stocks and exchange-traded funds trade on exchanges, regulated marketplaces that match buyers with sellers. In the United States the two best known are the New York Stock Exchange and Nasdaq, and many trades also happen on other electronic venues. As an individual investor you never deal with an exchange directly. You place an order with a brokerage, and the brokerage sends it to a venue for execution. Which exchange lists a company makes no practical difference to you.

The main US session runs from 9:30 a.m. to 4 p.m. Eastern time on business days. Many brokerages also offer pre-market and after-hours trading, but fewer people trade then, so prices can be less favourable and move more sharply. For a long-term investor there is rarely a reason to trade outside the regular session.

After a trade, the exchange of money and shares, called settlement, takes one business day for most US stocks and exchange-traded funds, a rule the Securities and Exchange Commission set in 2024. This matters mainly when you sell and want to move the cash out.

Mutual funds work differently. They do not trade during the day at all. Every order placed before the fund's daily cut-off, usually the 4 p.m. close, is filled at the same price: the fund's net asset value, calculated once after the market closes. Exchange-traded funds hold similar baskets of securities but trade throughout the day like stocks, so the order types below apply to them.

Order types and what each risks

When you buy or sell a stock or an exchange-traded fund, the order type decides how the trade is filled.

• Market order. Buy or sell now at the best price available. It almost always fills, but you do not control the price. In a fast-moving or thinly traded security, the price can be noticeably worse than the last one you saw.
• Limit order. Buy at or below a price you set, or sell at or above it. You control the price, but the order may not fill if the market never reaches it.
• Stop order (stop-loss). Becomes a market order once the price touches a trigger you set. It is often used to limit a loss, but in a sudden drop it can sell well below the trigger, and a brief dip can trigger a sale just before a recovery.
• Stop-limit order. Becomes a limit order at the trigger. You avoid selling far below your price, at the risk of not selling at all.

Orders can also be set to expire at the end of the day or to remain open until cancelled. For most investors buying a widely traded fund during normal hours, a limit order set at or near the current asking price gives price protection at almost no cost.

Reading a quote

A stock or fund quote packs several numbers into one line. Here is what each means.

• Last price. The price of the most recent trade.
• Change. How far the last price is from the previous day's closing price, in currency and percent.
• Bid and ask. The bid is the highest price a buyer is currently offering; the ask is the lowest price a seller will accept. The gap between them is the spread. A market order to buy usually pays the ask, and a market order to sell receives the bid, so the spread is a cost of trading that never shows up as a fee. Widely traded securities have spreads of a fraction of a percent; thinly traded ones can be much wider.
• Volume. How many shares have traded today. High volume generally means narrow spreads and easy trading.
• Day range and 52-week range. The lowest and highest prices today and over the past year. They show how much the price moves, not whether it is cheap.
• Market capitalisation. The share price times the number of shares, as described in chapter 2.

Many brokerages now offer fractional shares, so you can invest a set amount in a fund rather than buying whole shares at whatever the price happens to be.

What the indexes measure

An index is a list of securities with a rule for weighting them, used to measure a part of the market. When the news says "the market", it usually means one of these.

• S&P 500. About 500 large US companies, weighted by their market value, together covering most of the value of the US stock market. It is the most common benchmark for US stocks.
• Dow Jones Industrial Average. Thirty large US companies, weighted by share price rather than company size, so a high-priced stock moves it more than a larger company with a lower share price. It is famous more for its age than for what it measures.
• Nasdaq Composite. Several thousand stocks listed on Nasdaq, heavily weighted towards technology.
• Russell 2000. Two thousand smaller US companies, the usual benchmark for small companies.
• Total market and international indexes. Broader lists covering nearly every listed US company, or companies in developed and emerging markets abroad.

An index fund simply buys what an index holds, so its return is the index's return minus the fund's small costs.

One detail matters when you compare returns. Headline index levels are usually price indexes: they ignore dividends. A total return index assumes dividends are reinvested. Over long periods the difference is large, as these two examples show.

With dividends reinvested the sum reaches about $76,123, compared with about $43,219 from price changes alone. The rates here are illustrations, but the lesson holds: when someone quotes how much an index rose, check whether dividends are included before comparing it with your own account.

Signals that make headlines

Financial news reports a stream of indicators. Knowing what they mean is useful; trading on them is a different matter.

• The VIX measures the volatility that options prices imply for the S&P 500 over the next month. It rises when investors are fearful.
• The yield curve compares short-term and long-term Treasury yields. When short rates are higher than long ones, the curve is called inverted, which has often come before recessions, though the timing has varied widely.
• Market breadth compares how many stocks are rising with how many are falling, showing whether a move is broad or driven by a few large companies.
• The put-call ratio compares bets on falling prices with bets on rising ones, a rough reading of mood.

These describe the market's mood today. None of them reliably tells an individual investor when to buy or sell, and decisions made from them usually mean trading more, paying more in spreads and taxes, and risking being out of the market on the days that matter most. A long-term plan built on a set mix and regular contributions does not need them.