Market Depth ("The Book") provides a quick snapshot of the current list of working orders at various price levels of electronic contracts traded on a real-time exchange. It provides a side-by-side view of buy and sell orders or Level 2 data for futures markets, giving you insight into the depth of liquidity in a given market. Add the Market Depth panel to a workspace by clicking on Trade in the main toolbar.
The top row is the "Top of the Book", with the best bid and ask price for the instrument. The left two columns show bid prices and sizes, and the right two columns show ask prices and sizes. As you go further down the rows, the prices get farther away from the current market price. This view gives you an simple overview of where the order activity is happening in the market, and can provide some insight into which direction the market is moving.