The Layer Bar displays the active layer on the left. The graphic next to the layer number indicates there is data on the layer, and what type it is. You can make a different layer active by selecting it from this list.
On the right, if the active layer is not an NC layer, the active D-code is displayed. The graphic next to the D-code number shows the shape of each aperture. All custom apertures are signified by an irregular shape with a "C" in the middle (the actual shape is not indicated.) You can make a different D-code active by selecting it from this list.
If the active layer is an NC layer, the active NC tool is displayed. If the Add|Break Tab command is in use, the currently active tab is displayed, with an icon that indicates its type. You can make a different tool or tab active by selecting it from this list.