To access your list of maps, click on the Maps icon on the left hand side of the screen:
Once you open a map by selecting it from the list of maps, the legend will show each layer of data in that map. You can turn these layers on and off clicking the green/grey dot to the left of each line.
Below is an example of the legend for a map. For any layers that have a complex style you can click the arrow to the right of the layer name to collapse the styles.