Depth charts are two axes.
Price and quantity.
Horizontal price and vertical quantity.

Left side (green): Purchase orders Indicates the quantity of assets that buyers are willing to acquire and the maximum price they agree to pay
Right side (red): Sell orders. Shows the volume sellers are offering and the minimum price they are willing to sell at.
Midpoint: The current price of the asset, where the last transaction took place.

support and resistance levels