The market depth chart is a visualisation of the top 25 bid/ask orderbook for one exchange (in this case Binance) orderbook. It puts all buy (bid) and sell (ask) orders into a chart and stacks them onto each other. To do that, market depth charts use an additional indicator: Sum. This indicator sums up all existing orders sorted by ascending (sell orders - red) or descending (buy orders - green) prices. It then displays the consolidated order values on a stacked area chart as shown below:

You can use the depth chart to easily visualise the size at the best bid or ask (where the two area charts meet) and how much you can buy or sell at a given price.

You can also easily visualise large buy or sell walls.

The chart below shows a large buy wall i.e. there are a lot of people or algo's willing to buy:

The chart below represents a sell wall i.e. there are a lot of people or algo's willing to sell:

In some cases, a market has multiple exchanges in the Markets page. In that case you can control which exchange to view the market depth chart for, as shown below: