(Optional) Enter a name (use only alphanumeric characters, underscores, or periods) and click "Apply".
Choose the method to create your polygon.
Draw polygon using the toolbar at the top left corner of the map.
Enter decimal latitudes and longitudes for vertices of polygon, separated by commas, then click "Create polygon". Use lon/lat < 0 for west/south. Lists must be the same length, with >2 values each, in the same order so that each latitude is paired with longitude.
Click "Browse" to find a shapefile. Select the "shp" file and all files with the same name but different extensions (e.g. dbf, prj, sbx...), then "Open". If the polygon does not load automatically, click "Create polygon" (NOTE: polygons with a large number of vertices may take several seconds to load). Warning: This will only use the first polygon in the shapefile, and disjoint polygons are NOT allowed.