Layers can contain map features: placemarks, lines, tracks, areas (v3.3 - currently in Beta) photos, and schema. All map features stored in the database are listed in the Layers tab. Map features can be managed here, including adding, deleting, and editing map feature information (Features cannot be exported from the Layers tab - see Exporting Map Features for more information).
The Layers tab also displays the map that features are linked to (see Importing Map Features for more information about linking map features). Alternatively, linked layer's map features can also be managed (including imported and exported) from within the Map View (see Managing Map Features for more information)