Zotero's Group Libraries feature allows you to share references with other Zotero users online. It's a great way to work on collaborative research projects.
'My Library' and 'Group Libraries' are entirely separate, and changes made to items in one library do not affect the other. You can't share a collection from your personal library; you must create a Group Library to work with collaborators on the same library.
Get set up with Group Libraries:
After creating or joining a Group Library, you will now have two sections in your Zotero collections pane: My Library and Group Libraries.