Create a new collection by clicking the yellow folder icon in the top left-hand corner of the interface. 

You can create folders and sub-folders. 

Items can exist in multiple folders simultaneously. 

To add an item to another collection, drag and drop it from "My Library" to the folder of choice. 

Duplicates happen, especially when you're dealing with bulk imports. To eliminate duplicate resources, select the Duplicate Items tab in your Library bar. 

Select a duplicate entry. Use the selection box on the right-hand side of the interface to switch between items. Sometimes Zotero makes a mistake and flags items as duplicates that are truly not duplicates. Sometimes one record has more complete metadata than another. 

You can also classify items in your library with tags. It's another way to describe and filter items, surface relevant concepts, and filter keywords at a glance. Tags are sometimes imported with documents, but may be manually added. 

Tip: You can assign colors to hero tags like To Read or For Capstone.

If you want to remove an item from a file or your library, right-click the item for a pop-up menu. You can either Remove Item from Collection or Move Item to Trash.