Out of the box, if you’ve not configured any Portals or Organization accounts, selecting the ArcGIS Online menu option pops-up a dialog window to select/search content. If you add your own Portal or Org using the ArcGIS Admin tool, clicking that menu item shows the same window but just with the content in your Portal or Org. For my client, that tool is grayed out in their Desktop sessions in Test and we would like to know what enables it.
Here is more on the tool:
http://desktop.arcgis.com/en/arcmap/10.3/map/working-with-arcmap/adding-data-from-arcgis-online.htm
