Select the layer you want to be the primary focus of the map from the drop down list. Information about the layer will appear on the right.
Select the base map and options to use for your widget. Pan and zoom until you have the map center and zoom level you want your embedded map to start with. You may have to zoom in to see some layers.
Customize the size of your map by clicking on a size or entering your own custom dimensions. Paste the embed code in your site and enjoy your new map!