Tier 2 · Essentials · Stocks · Module ST.1
Exchanges, indices, and sectors
How stock markets are organised — exchanges and trading hours, market capitalisation, indices, and sectors — and how retail traders actually access shares.
Lesson 1 of 1 · 6 min read
A share is a small piece of ownership in a company. Unlike forex, where the market never truly closes, stock markets are organised around exchanges with opening bells, closing auctions, and thousands of individual companies grouped into indices and sectors. Understanding that structure helps you choose what to trade, when to trade it, and how to read the market's mood on any given day.
What you'll learn
- What stock exchanges do and how their trading day is structured
- Market capitalisation and why company size matters to traders
- What indices are and why traders watch them before individual stocks
- The eleven standard sectors, and cyclical vs defensive behaviour
- The main ways retail traders access stocks — and what each means for you
1. Exchanges and the trading day
A stock exchange is a regulated, central marketplace where buy and sell orders for listed shares are matched. The largest in the world include the New York Stock Exchange (NYSE) and Nasdaq in the US, plus major exchanges in London, Tokyo, Shanghai, Hong Kong, and Europe (Euronext, Deutsche Börse).
Because exchanges are centralised, stocks have a real order book and real volume — unlike spot forex (see Buyers, sellers, order books, price discovery).
The US trading day (New York time)
| Session | Hours | Character |
|---|---|---|
| Pre-market | Early morning until 9:30 a.m. | Thin liquidity, wide spreads, reacts to overnight news |
| Regular session | 9:30 a.m. – 4:00 p.m. | Deepest liquidity; opening and closing auctions set key prices |
| After-hours | After 4:00 p.m. | Thin liquidity; many companies report earnings here |
The first and last hour of the regular session usually see the heaviest volume. The middle of the day is often quieter.
2. Market capitalisation
Market capitalisation (market cap) = share price × shares outstanding
(Illustrative.) A company with 2 billion shares trading at $75 has a market cap of $150 billion.
| Category | Typical size (guide only) | Character |
|---|---|---|
| Large cap | Above about $10 billion | More liquid, more analyst coverage, often steadier |
| Mid cap | About $2–10 billion | Growth potential with moderate liquidity |
| Small cap | Below about $2 billion | More volatile, thinner liquidity, larger gaps |
For traders, size matters mainly through liquidity: large caps have tighter spreads and absorb orders more easily. Small caps can move much more, in both directions — and can be hard to exit in a hurry.
3. Indices
An index tracks the combined performance of a group of stocks. The most watched include:
| Index | What it tracks |
|---|---|
| S&P 500 | About 500 large US companies — the main benchmark for US stocks |
| Nasdaq 100 | 100 of the largest non-financial companies listed on Nasdaq — technology-heavy |
| Dow Jones Industrial Average | 30 large US companies |
| FTSE 100, DAX, Nikkei 225 | Large companies in the UK, Germany, and Japan |
Traders watch indices even when trading a single stock because most stocks move partly with the whole market. A strong earnings report may still see a stock fall on a day when the whole market sells off. You'll study how indices are built in the Indices & Futures track.
4. Sectors
Companies are grouped into sectors by what they do. The widely used Global Industry Classification Standard (GICS) has 11 sectors:
Communication Services · Consumer Discretionary · Consumer Staples · Energy · Financials · Health Care · Industrials · Information Technology · Materials · Real Estate · Utilities
Cyclical vs defensive
| Type | Examples | Tends to do well when… |
|---|---|---|
| Cyclical | Consumer Discretionary, Industrials, Financials, Materials, Energy | The economy is growing and confidence is high |
| Defensive | Consumer Staples, Utilities, Health Care | Growth slows — people still buy food, power, and medicine |
When money moves from one group to another as the economic outlook changes, it's called sector rotation. Comparing sector performance tells you what the market is betting on.
5. How retail traders access stocks
| Route | What you own | Things to know |
|---|---|---|
| Shares (cash account) | Real ownership, voting rights, dividends | No leverage by default; you can't lose more than you invest |
| Margin account | Real shares bought partly with borrowed money | Interest on the loan; margin calls if prices fall |
| CFDs on shares | A contract on the price — no ownership | Leverage, overnight financing, dividend adjustments; widely available outside the US but restricted for US residents |
| ETFs | A fund holding many shares (for example an index or sector) | Diversified exposure through a single instrument |
Common beginner mistakes
- Trading in pre-market or after-hours without realising how thin liquidity is.
- Ignoring the index and sector when trading an individual stock.
- Assuming a stop-loss protects against overnight gaps.
- Trading small caps with large-cap position sizes.
- Using CFDs without understanding they don't give ownership, and carry financing costs.
Key terms
| Term | Meaning |
|---|---|
| Stock exchange | A regulated central market for trading listed shares |
| Regular session | The main trading hours of an exchange |
| Market capitalisation | Share price × shares outstanding |
| Index | A measure of the combined performance of a group of stocks |
| Sector | A group of companies in the same line of business |
| GICS | The Global Industry Classification Standard (11 sectors) |
| Sector rotation | Money shifting between sectors as the economic outlook changes |
Practice
- Look up the market cap of three companies you know. Classify each as large, mid, or small cap.
- Compare a large-cap stock's typical spread with a small-cap stock's during the regular session.
- For the last month, compare the S&P 500 with a defensive sector ETF and a cyclical sector ETF. Which led?
- Check how your broker offers stocks — real shares or CFDs — and what the overnight costs are.
Quick recap
- Stocks trade on centralised exchanges with real order books, volume, and defined sessions.
- The first and last hour of the regular session are usually the most active; gaps happen overnight.
- Market cap drives liquidity and volatility.
- Indices and sectors set the backdrop for individual stocks.
- Know whether you're trading shares or CFDs — and the risks each carries.
Educational content only — not financial advice. Trading involves substantial risk of loss. Practise on a demo account before risking real money.
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