After you have filled in your "Location Details", you can fine tune the map position shown. Zoom and pan the map with the map controls in the upper left corner of the map to have it just the way you would like it displayed with your ad. Left click to place a marker on the map.

TIP: If you wish to mark the general area where your item is located but not reveal the exact location of your house you can place a marker on the nearest landmark to your house, like a shop, or public green area.