Zotero

Folders in Zotero are called collections. You can put an item in multiple collections without duplicating it. All items are always accessible from the main library.

Setting Up Collections

Click the folder icon under the library panel to create a new collection.

You will see a window appear for you to rename the file and choose where you would like to create the collection in.

Once you create a collection, it will appear on the left-hand side under "My Library"

Right click a collection to create a subcollection. 

After clicking "New Subcollection," You will see a window appear for you to rename the subcollection and choose where you would like to create the collection in.

After creating the subcollection, it will appear within the collection (folder) under "My Library." 

Drag and drop to add items to collections. You can also add items to collections by right clicking your item(s) and selecting where you would like them to be placed. 

You can also add items directly to collections when you use the browser connector to add items to your library.

By default, items in subcollections do not appear in the top level collection folder. To make items in subcollections visible, go to View > Show Items in Subcollections.