A legend is available that defines the symbology for the layers you have turned on. (Off layers will not display in the legend).
To access the legend, click the Panel Actions Menu and choose Show Legend.
The legend will appear, replacing the Layer List
You can toggle between the legend and your selection using the tabs at the bottom of the left-side pane.
To get back to the layers list, you must click again on the Panel Actions Menu and this time choose Show Layer List