Before you can add your placemarker you need to create an account on Google & sign in. Then click this link...
http://maps.google.com/maps/ms?hl=en&ie ... 392843f876
Then click the Edit button on the left hand panel, zoom into the place you want to mark & use the placemarker tool in the map panel to mark it. You can add text to the placemarker if you wish & if you select Rich Text you can add a picture. When you are done click the Save button on the left.