public class PortalItem : OnlineItem, ArcGIS.Desktop.Core.IMetadata, System.ComponentModel.INotifyPropertyChanged, System.ICloneable  

{
  // Creates an Item from an existing portal item base on its ID
  string portalItemID = "9801f878ff4a22738dff3f039c43e395";
  Item portalItem = ItemFactory.Instance.Create(portalItemID, ItemFactory.ItemType.PortalItem);
  // use portalItem;
}

{
  // Creates an Item from an existing portal folder base on its ID
  string portalFolderID = "39c43e39f878f4a2279838dfff3f0015";
  Item portalFolder = ItemFactory.Instance.Create(portalFolderID, ItemFactory.ItemType.PortalFolderItem);
  // use portalFolder;
}

{
  FolderConnectionProjectItem projectfolderConnection = Project.Current.GetItems<FolderConnectionProjectItem>().First();
  var folderConnectionContent = projectfolderConnection.GetItems();
  var folder = folderConnectionContent.FirstOrDefault(folderItem => folderItem.Name.Equals("Tourist Sites"));
  var folderContents = folder.GetItems();
  //use folderContents;
}

{
    //Basemaps stored locally in the project. This is usually an empty collection
    //Note: Needs QueuedTask to run
    string localBasemapTypeID = "cim_map_basemap";

    var mapContainer = Project.Current.GetProjectItemContainer("Map");
    mapContainer.GetItems().Where(i => i.TypeID == localBasemapTypeID).ToList();

    //portal basemaps. If there is no current active portal, the usual default
    //is arcgis online
    var portal = ArcGISPortalManager.Current.GetActivePortal();
    var portalBaseMaps = await portal.GetBasemapsAsync();

    //use one of them...local or portal...
    //var map = MapView.Active.Map;
    //QueuedTask.Run(() => map?.SetBasemapLayers(portalBaseMaps[0]));  
}

{
  var activePortal = ArcGISPortalManager.Current.GetActivePortal();
  var owner = activePortal.GetSignOnUsername();
  var activeUserContent = await activePortal.GetUserContentAsync(owner);
  //Get content for a specific folder (identified by its folder id)
  //var userContent = await portal.GetUserContentAsync(owner, folderId);

  //Get all the folders
  foreach (var pf in userContent.PortalFolders)
  {
    //Do something with the folders

  }
  //Get all the content items
  foreach (var pi in userContent.PortalItems)
  {
    //Do something with the portal items
  }
}