There are three types of groups in Zotero.
Zotero's Groups feature allows you to share references with other Zotero users online. It's a great way to work on collaborative research projects.
You now have two sections in your Zotero collections pane: My Library and Group Libraries.
Personal and group libraries are entirely separate, and changes made to items in one library do not affect the other. You can drag items back and forth libraries to copy items.
To join an existing Zotero library, search for it at zotero.org/groups or be invited by the group’s owner.