mvn -e clean install package
The final .swf will be in the directory geoportalMinOpenscales/geoportail-api-fx-examples/target. You may have to rename the file according to his name in the html file. The final .swc will be in the directory geoportalMinOpenscales/geoportail-api-core/target.
Open FlashBuilder, File/New/Flex Project.
Give a name to the project. Here, it will be called 'projet_api_geoportail'.

The project will look like the following arborescence :
