Exchanges, brokers, and the order book

You do not trade on an exchange directly. You send an instruction to a broker, the broker routes it to a venue, and a matching engine pairs it with an opposite instruction. Ownership is then recorded and settled, typically a business day or so later depending on the market.

Every link in that chain has rules and costs: commissions, currency conversion, regulatory fees, and the spread. Beginners usually notice only commissions, which are often the smallest of them.

The order book holds resting buy orders (bids) and sell orders (asks). The highest bid and the lowest ask form the quote. The distance between them is the spread — the immediate cost of changing your mind, because you buy at the ask and sell at the bid.

Liquidity describes how much you can trade without moving the price. Large, heavily traded companies have pennies of spread and deep books. Thinly traded ones can have wide spreads where a single order visibly jumps the price.

Quotes update as orders arrive, cancel, and execute. Nothing about the underlying business changed in that second; the balance of willing buyers and sellers did. This is why intraday price noise carries very little information for a long-horizon learner.