The assembly editor's catalog on the left side contains modules, assemblies, and subassemblies that are public, yours, and shared with you:
The catalog can be resized and open/closed by clicking or dragging the splitters:
The catalog can also be opened/closed and refreshed via the menu options under the More menu at the top right:
The "Community" tab of the catalog contains all public content.
The "Mine" tab of the catalog contains content you created and private content created by other accounts that is shared with you:
The catalog can be searched in various manners:
The "community" and "mine" catalogs can be searched together or separately for modules, assemblies, assemblies containing text within module fields, and assemblies having notes containing text.
Mouse over items in the catalog to view any help information about the item. Help information appears at the bottom here:
Right-click on items in the catalog to view options: