A price is an agreement, not a fixed value
Picture a farmers’ market. A seller shouts “three euros a kilo for apples.” A shopper says “I’ll pay two-fifty.” If they settle at two-eighty, that is the price — but only for that single deal, in that moment. A stock exchange works the same way, only faster and thousands of times in parallel. The price you see on screen is simply the price of the most recent completed trade.
A key point for beginners: the price is not an official valuation or a “correct” number. It is a compromise that is renegotiated constantly. That is why the same asset can trade at slightly different prices within seconds.
The order book: where buyers and sellers wait
An order book is a live list of every open buy and sell request. On one side sit the buyers with their prices, on the other the sellers. Two terms are worth knowing:
The highest price any buyer is willing to pay right now. The “demand” side.
The lowest price any seller is willing to accept. The “supply” side.
The gap between bid and ask is the spread. Think of it as a hidden trading cost: buy at the ask and immediately sell at the bid, and you lose the spread. For heavily traded assets like large stocks or bitcoin the spread is tiny; for rarely traded ones it can be noticeably wide.
How the price actually moves
A price does not rise “because a stock is worth more.” It rises because buyers grow more urgent. Suppose every sell offer up to €100.00 has been bought. The next buyer who wants to trade immediately must take the next offer at €100.05. The new price is now €100.05 — the market has “walked up.” This process of eating through the order book is called order flow.
Rule of thumb: it is not the number of buyers that moves a price, but their urgency. One large, impatient buyer can move the price more than a hundred patient ones.
Market orders move, limit orders wait
There are two basic order types, and the difference explains almost all short-term movement. A limit order sets a price and rests in the order book — it “provides” liquidity and waits patiently. A market order says “right now, whatever the price” and takes the best available offers — it “takes” liquidity and moves the price. Whenever a move is fast and sharp, aggressive market orders are usually behind it.
In practice, for a beginner: a limit order gives you control over price but risks never filling. A market order guarantees a fill but, in illiquid markets, can cost noticeably more than you expected (this gap is called slippage).
Why liquidity changes everything
Liquidity means: how many orders are waiting around the current price? In a deep, liquid market, large amounts of buy and sell orders sit closely stacked. A single order barely dents it, and the price moves in calm, small steps. In a thin market, big gaps open in the order book — the same order then leaps across several price levels and creates a violent swing.
This explains why small cryptocurrencies or obscure stocks swing so wildly, while an index like the S&P 500 usually moves gently. It is not that these assets are “more nervous” — they simply have less liquidity to cushion the moves.
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Frequently asked questions
What is the difference between bid and ask?
The bid is the highest price a buyer is currently willing to pay. The ask (or offer) is the lowest price a seller is willing to accept. The current “price” usually sits somewhere between them and is set the moment a buyer and seller meet.
What is the spread?
The spread is the gap between the bid and the ask. A tight spread (a few cents) signals high liquidity and lots of active traders. A wide spread signals thin trading and a higher hidden cost every time you buy or sell.
Why does a price move at all?
A price moves when one side wants to trade more urgently than the other. If more buyers want to buy right now than sellers are offering at the current price, buyers climb the order book and the price rises. When sellers are more eager, it falls.
What does liquidity mean?
Liquidity describes how easily you can buy or sell without moving the price much. A liquid market (such as Apple shares) always has plenty of buy and sell orders. In an illiquid market, even a mid-sized order can push the price noticeably.
What is the difference between a market and a limit order?
A market order buys or sells immediately at the best available price — you get filled, but not necessarily at your ideal price. A limit order sets a price and waits for the market to reach it — you get your price, but maybe no fill.