I may be very silly, but I can't find (on the mac version) how to paste in a new feed
I find also very difficult to place correctly a new folder (it usually falls inside another one with no option to deselect all and place it at "root" level
(otherwise, thumbs up for this new mac release ;-)
For the new folder, please note that you may create a new "Category" which will be on the same level as the selected one and a "Sub-Category" which will be a folder as child of the selected one.
For creating a new favorite, you have to select "New > Favorite" and paste its adress, or open the feed and select "Add to Favorites" from the "Newsfeed" menu. Its also possible to drag an opened feed into the tree of favorites.