Change the three points in the "three_points+icon.kml" file, the center and the size of the map.
In KML, points are entered as longitude / latitude. Google Maps provides pointsas latitude / longitude.
In order to view the points, the KML file needs to be online. It is not possible to display the file locally.
That means this code and the KML file must be uploaded to the server before the points will be displayed.