Order books facilitate trading by showing all buy and sell orders in real-time. They help traders understand supply and demand dynamics, allowing them to make informed decisions based on current market conditions. Orders are usually categorized as 'bid' (buy orders) and 'ask' (sell orders), and they can be displayed in different formats (e.g., limit orders, market orders). In a fully functioning market, an order book helps ensure there is a transparent and fair trading atmosphere.