Drawing a polygon in the map is quite simple. Follow the steps below to draw a polygon on the map, and download the resulting polygon in .KML file format.
Start the polygon drawing tool by clicking on the "Draw Polygon" button (looks like a pencil):
Draw the polygon by clicking on the map where you would like to start drawing, then holding the left mouse button, and moving your mouse to draw a freehand polygon
Download the polygon as a .KML file by clicking on the "Download Last Polygon." This will download whichever polygon was drawn last.
The polygon will download as a .KML file:
Upload that same .KML file into the "Related File or Image" part of the map if you would like to use the polygon as part of your comment.
Also, you can open the KML file in Google Earth if you wish.