I am using the GoogleMaps/GoogleMap web block and would like to know how to put on marker on the page.
The component itself provides a demo which you can find running here.
If you open the espace GoogleMapsDemo you can see how it's adding the markers.
Hope this helps
Also, just to make sure, when you say "GoogleMaps\GoogleMap", you meant the block below, right?
If so, Guilherme was right: there is a Demo module included with the component that provides examples on how to use it. You can use the action or the "AddMarker" block.