You can organize items in the Library panel using folders. When you create a new symbol, it is stored in the selected folder. If no folder is selected, the symbol is stored at the root of the library.
Create a new folder
Open or close a folder
Double-click the folder, or Select
the folder and select Expand Folder or Collapse Folder from the
Panel menu for the Library panel.
Open or close all folders
Move an item between folders