On your left-hand side you'll find all your Libraries, those that are yours only and the shared ones.
Here you'll find all the items in your Library. Right-click on My Library to create a new Collection.
Collections and Subcollections allow you to keep your information organized. Collections are useful for filing items in meaningful groups (e.g., items for a particular research project or on a specific topic). You can import items directly to a specific collection or add them to collections after they are already in Your Library. Items can belong to multiple collections and subcollections. Adding an item to multiple collections will not duplicate the item.
Under My Publications you could share your own research work (including items, notes, and attachment files) publicly with the world. More information on the "My Publications" collection is available here.
You can create collaborative or interest groups. Shared group libraries make it possible to collaboratively manage research sources and materials.
Group Libraries can be Public or Private.
Duplicate Items: The Duplicate Items collection shows items that Zotero has identified as potential duplicates. You can use this collection to review and merge duplicate items.
Tag Selector: Found at the bottom part of the left column. It shows all the tags that have been assigned to the items currently shown in the central column. You filter by clicking on one or more tags. You can rename and also assign colors to tags. All automatic tags from a library can be deleted by clicking “Delete Automatic Tags in This Library”, the multi-color button in the lower-right corner of the tag selector. 
Disclaimer: The contents and links referenced in this guide are provided only for information and do not constitute policies, recommendations or opinions of the ILO.