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);

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

var folderConnectionContent = projectfolderConnection.GetItems();
var folder = folderConnectionContent.FirstOrDefault(folderItem => folderItem.Name.Equals("Tourist Sites"));
var folderContents = folder.GetItems();

//Basemaps stored locally in the project. This is usually an empty collection
string localBasemapTypeID = "cim_map_basemap";
var localBasemaps = await QueuedTask.Run(() =>
{
  var mapContainer = Project.Current.GetProjectItemContainer("Map");
  return 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 portal = ArcGISPortalManager.Current.GetActivePortal();
var owner = portal.GetSignOnUsername();
var userContent = await portal.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
}