How Trading Actually Works

People say "I bought some stock today" like it is just tapping a button. But behind that tap, a chain of people, computers, and rules moves your money safely to a stranger on the other side of the trade. This chapter pulls back the curtain: what a broker is, how the two main account types work, what happens after you press "buy," and how to use the main order types — the exact instructions you give when you trade.

What Is a Broker?

A broker is a licensed company that gives you access to the stock market. You cannot walk up to an exchange and buy shares yourself — exchanges only deal with member firms. Your broker is your doorway in, like the agent who gives you access to house listings and makes the deal official, for stocks and options (contracts based on a stock's price — covered in the options chapters).

Your broker sends your orders where buyers and sellers meet, holds your money and investments safely separated from its own money, and keeps records of everything you own.

US brokers are regulated — watched over — by the SEC (Securities and Exchange Commission, the main federal market regulator) and FINRA (the Financial Industry Regulatory Authority, an industry watchdog). Customer assets are protected by SIPC insurance (Securities Investor Protection Corporation) up to $500,000, including up to $250,000 in cash, if the broker itself fails. Be clear: SIPC protects you if the firm collapses — not if your investments go down in value.

How to Pick a Broker

There is no single "best" broker — only the best fit for you:

What you can trade. Some brokers offer only stocks and funds; others also offer options and futures (contracts based on the future price of things like oil or indexes).
Costs. Many brokers charge $0 commission on stock trades today, but options and futures usually carry per-contract fees.
The platform. Can you find your balance, positions, and the order screen without hunting?
Education and practice tools. Good beginner brokers offer lessons and paper trading — a practice account with fake money, covered at the end of this chapter. Some open accounts at $0; others ask for a deposit.

The Two Main Account Types: Cash and Margin

Cash account

A cash account is the simple one. You trade only with money you deposited that has settled — finished moving through the banking system and become fully yours to use. Deposit $500 and you can buy up to $500 of stock. You can never owe the broker money or be charged interest. One quirk: money from a sale also needs time to settle before you can spend it again, and re-buying with unsettled money can trigger a warning called a good faith violation.

Margin account

A margin account lets you borrow money from your broker to buy more than your own cash allows. Borrowing to invest is called buying on margin, or using leverage — a little of your money controlling a bigger position.

Example: you have $1,000. In the US, the starting rule (called Regulation T, or Reg T) lets you borrow up to another $1,000, controlling $2,000 of stock. If it rises 10%, your position is worth $2,200 — a $200 gain on your $1,000, or 20%. But if it falls 10%, you lost $200 — 20% of your money — and you still owe the borrowed $1,000 plus interest (charged on the loan, like a credit card). If the fall gets bad enough, the broker issues a margin call — a demand to deposit more money right away — and can even sell your investments without asking, to protect its loan.

Margin accounts also unlock short selling (betting a stock will fall) and many options strategies — plus an extra rule day traders must know:

How You Actually Open an Account

The process is similar at almost every US broker. You apply online, giving your name, address, date of birth, Social Security number, and employment info — not nosiness: federal law (called Know Your Customer rules) requires brokers to verify who you are, partly to prevent fraud. You choose cash or margin; margin requires a separate agreement accepting the borrowing risks in writing. You answer risk questions about income, net worth, and experience, which decide your approvals — options trading, for example, comes in levels. Then you fund the account, usually by bank transfer, which can take a few business days to settle.

How a Trade Travels: From Your Tap to the Exchange

Say you decide to buy 10 shares of a fictional company, Acme Corp, ticker ACME. Here is its journey:

Step 1 — You place the order. In the app you pick the stock, the share count, and the order type (covered below), and tap "buy."
Step 2 — Your broker checks and routes it. Its computers confirm you have the money, then send the order to a venue — a place where trades happen, such as a stock exchange (a regulated marketplace like the New York Stock Exchange or Nasdaq).
Step 3 — Your order meets a seller. Another investor wants to sell 10 shares of ACME. Every buy needs a sell; the venue's computers match you in a fraction of a second, and the trade prints publicly — that is why prices update all day on financial websites.

Step 4 — The trade settles. Money and shares officially change hands. For US stocks this takes one business day, called T+1 (trade date plus one day) — the standard since May 2024. You see the shares right away, but the final transfer completes on T+1.

The Three Prices on Every Stock: Bid, Ask, and Last

Every stock quote shows three prices. Beginners often notice only one — and it costs them.

Bid price — the highest price a buyer is offering right now. Sell immediately, and this is roughly what you get.
Ask price (also called the offer) — the lowest price a seller is asking right now. Buy immediately, and this is roughly what you pay.
Last price — the price of the most recent completed trade. This is the big number on TV and in apps. It is history, not a promise of your price.

The gap between bid and ask is the spread. Example: ACME shows a bid of $49.98 and an ask of $50.02. The spread is $0.04. Buy at the ask and instantly sell at the bid, and you lose 4 cents a share before the stock even moves. Popular stocks have spreads of a penny or two; quiet, rarely traded stocks can have wide spreads — a hidden cost.

Buying Power: How Much You Can Actually Trade

Your buying power is the amount your broker lets you commit to trades right now. In a cash account it is basically your settled cash: $500 settled means $500 of buying power. In a margin account it includes borrowable money — $1,000 of cash might show $2,000 of buying power under Reg T. Buying power drops the moment you place an order, because the broker reserves the money.

Order Types: The Instructions You Give Your Broker

An order is not just "buy." It is a set of instructions: what, how much, and under what conditions.

Order Type	What It Means in Plain Words	When Traders Use It
Market order	Buy or sell right now at the best available price, whatever it is	When speed matters more than the exact price
Limit order	Buy or sell only at your chosen price or better — never worse	When you refuse to overpay or undersell
Stop order (stop-loss)	Once the price touches your trigger, it becomes a market order	To limit a loss automatically if a trade goes wrong
Stop-limit order	Once the price touches your trigger, it becomes a limit order at your chosen price	To control the exit price — but it may not fill at all
Trailing stop	A stop that follows the price by a set amount or percentage	To lock in gains while giving a trade room to run
Day order	Cancels at the end of today's session if it does not fill	The default; for prices that only make sense today
GTC order (Good 'Til Canceled)	Stays active until it fills or you cancel it (brokers cap this, often ~90 days — check yours)	When you will wait days or weeks for your price

Limit order — "my price or nothing"

A limit order sets a ceiling for buys and a floor for sells. Example: ACME trades at $50.10, but you only want it at $49.50. Place a limit buy at $49.50: you buy only if the price falls there or lower — and maybe never, if it never gets there. Certainty about price; no certainty about filling. For beginners, this is the safest default.

Stop order — "get me out if I'm wrong"

A stop order sleeps until the stock trades at your stop price, then wakes up as a market order. Its classic use is the stop-loss: buy at $50, place a stop-loss at $46, and if the stock falls to $46 your shares sell at the next available price — maybe $46, maybe lower in a fast drop. It limits your loss; it does not promise an exact exit price.

Stop-limit order — control, with a catch

A stop-limit order has two prices: the stop triggers it, the limit controls it. Stop at $46, limit at $45.50: once the stock hits $46, sell — but only at $45.50 or better. The catch: if the stock crashes straight through $45.50 — called gapping, jumping past a price without trading there, often overnight on news — it may never fill.

One more worth knowing: a trailing stop moves with the price. Set one $3 below the price on a $50 stock — the stop sits at $47 — and if the stock climbs to $58, the stop climbs to $55. It never moves backward, and it can be set as a percentage.

Commissions and Fees: The Small Print That Isn't Small

Many US brokers advertise $0 commissions on online stock and ETF trades. That is real — but trading is not free. Options usually cost a per-contract fee (commonly around $0.50–$1.00 per contract). Futures carry per-contract commissions plus exchange fees. Margin interest is charged daily on borrowed money at rates that vary widely, and tiny regulatory fees are passed through on trades.

Fractional Shares: Start Small, for Real

A fractional share is a slice of one share. Some famous companies trade at several hundred dollars a share. Many brokers now let you invest by dollar amount instead: put in $25 and own $25 worth of the stock, even if one full share costs $500 — you own 0.05 shares. If it pays a dividend (a cash payment a company sends its shareholders), you get your proportional slice. Not every broker offers them, so check yours.

Paper Trading: Practice With the Training Wheels On

Paper trading (also called simulated trading) is a full practice account: real live prices, fake money. You place real order types, watch fills, and track wins and losses — and risk nothing. Use it to practice each order type above until it is boring, and make your first mistakes for free.

Common Beginner Mistakes

Using market orders on everything. On a quiet stock with a wide spread, a market order can fill at a terrible price. Use limit orders as your default.
Opening a margin account on day one "for the features." Borrowing and interest are not features a beginner needs. Learn in cash first.
Placing a GTC order and forgetting it. It can fill weeks later, when you no longer want the trade.
Skipping paper trading. Refusing free lessons and paying for them with real losses is the most expensive habit in trading.

Chapter Summary

A broker is your licensed doorway to the market — regulated by the SEC and FINRA, with SIPC protection if the firm fails.
A cash account trades only settled money: no debt, no interest. A margin account lets you borrow (leverage), magnifying gains and losses, charging interest, and risking a margin call.
A trade travels: you → broker → exchange or venue → matched seller, then settles T+1.
Every quote has a bid, an ask, and a last price; the gap between bid and ask is the spread — a real cost.
Buying power is what you can commit: settled cash in cash accounts; cash plus borrowable funds in margin.
Order types: market (now, any price), limit (my price or nothing), stop (trigger, then market), stop-limit (trigger, then limit), trailing stop, day vs GTC.
Fractional shares let you invest by dollar amount; paper trading lets you practice with fake money first.

Check Yourself

What does a broker do for you, and who regulates US brokers?
You have $1,000 in a margin account and buy $2,000 of stock that falls 10%. Roughly how much have you lost, and what do you still owe?
A stock shows a bid of $30.00 and an ask of $30.06. What is the spread, and which price do you roughly pay if you buy immediately?
You bought at $80 and want automatic protection if the price falls to $72, accepting whatever price the market gives then. Which order type fits, and what does it become when triggered?
What does T+1 mean, and when did it become the US stock standard?

Show answers

Answers: 1) It routes your orders to exchanges, holds your money and investments, and keeps your records; US brokers are regulated by the SEC and FINRA, with SIPC protection if the firm fails. 2) About $200 — 20% of your $1,000 — and you still owe the $1,000 loan plus interest. 3) $0.06; you pay roughly the ask, $30.06. 4) A stop order (stop-loss) at $72; at $72 it becomes a market order and fills at the next available price. 5) The trade settles one business day after the trade date; US standard since May 2024.