Output layout of an artifact is displayed in a tree. You can edit it with Alt+Ins and Delete shortcuts, and by using drag-and-drop.
You can build artifact at any time from the main menu (Build | Build Artifact | <artifact name>), or you can automate it with the use of Build on make option in artifact settings, and Build Artifacts option in run configuration settings:
These features will be available in the next Maia EAP (around next Monday). Packaging configurations of existing JavaEE facets are migrated to artifacts automatically.