Here is how we used it.
1. Added Editor Widget in xaml.
2. We added feature service in code behind and explicitly initialized it.
3. In the initialized event, pasted following code
[PHP]
#region For editing
currentApps.Tools.EditorWidget.Map = currentApps.MapXaml.MyMap;
currentApps.Tools.EditorWidget.LayerIDs = currentApps.EditalbleLyrIDs;
currentApps.Tools.EditorWidget.GeometryServiceUrl = currentApps.WebconfigVrbls.GeomServiceURL;
currentApps.Tools.EditorWidget.Continuous = false;
currentApps.Tools.EditorWidget.ShowAttributesOnAdd = true;
currentApps.Tools.EditorWidget.AutoComplete = true;
currentApps.Tools.EditorWidget.EditCompleted += new EventHandler<Editor.EditEventArgs>(EditorWidget_EditCompleted);
#endregion For editing
[/PHP]
4. Widget is ready to use.
Hope this helps.