Widgets tab
http://resources.arcgis.com/en/help/flex-viewer/concepts/
Use this tab to specify the functionality for the new application. Listed at the top of the dialog are the available core GIS functionality widgets that can be added. At the bottom of the dialog are four widgets which are included in the new application by default, but can be removed or modified: Bookmarks, Geocode, Draw and Measure, and Print. These widgets are contained within the widget tray of the application. To add a widget, simply select it and click the Include button. The Widget tab dialog will change to display the specific configuration options available for the selected widget. Once the configuration options are set and confirmed, the dialog will return to the widget catalog display.
Properties of a widget can be changed after adding it to the new application by clicking the edit button (pencil icon) for the widget.