Most of the time you will add new objects by popping up the menu on the nodes in the tree on the left pane. However, the new object will always appear at the end of the folder. If you want to add a new object at a specific position in the folder, you'd better use the popup menu on the objects in the folder editor on the right. The popup menu of the folder editor provides 'New before' and 'New after' functions, each showing the same sub items.
Adding a new object at a specific position
If you select an object in the table you can also use buttons in the toolbar on top of the folder editor. The button is to add a new object before the selected object, the button is to add a new object after the selected object.
Adding a new object in the table using the buttons
If no object is selected in the table these buttons change to and to add the new object at the beginning or at then end respectively.