How do you add a marker to a Google map? I know it has something to do with map.addOverlay(marker), but what value should marker be? Here's what I've got so far:

Code JavaScript:
    <script type="text/javascript">
        function load() {
            if (GBrowserIsCompatible()) {
                  var map = new GMap2(document.getElementById ("map"));  
                  map.addControl(new GSmallMapControl());
                  map.setCenter(new GLatLng(-27.462719, 153.029122), 16);
            }
          }
    </script>