The order in which the layers are listed in the legend is also important. The layers at the top of the legend are drawn on top of those below it. Layers that form the background of your map are listed at the bottom of the legend. After selecting the layers to be on or off hit the button to redraw the map with the new settings. Make a layer active by clicking on the radio button in the legend.
Many operations work only on active layers.
You may only have one layer active at a time. By clicking and holding the mouse button down in the upper left corner and dragging a red box over to the bottom right and releasing the mouse button the map will be redrawn in the area you outlined with the red box. Zooming in to an area will display more details in the map. Zooming in too much will not display any more detail and could result in a blank map. Click the Identify button.