Zotero allows you to create groups of Zotero users. Groups have their own libraries, separate from your personal Zotero library, which you can use to share items with classmates or colleagues.
To participate in a group, each member should:
One member of the group will be the owner. They can create the group by logging in to zotero.org and navigating to the Groups page. Then:
After creating the group, you will have the option to change the group settings. The default settings should be fine for most purposees.
To add members, navigate to the "Members Settings" page for the group. Under the "Member Invitations" heading, you will see the option to "Send More Invitations."
Enter email addresses or Zotero user names for each member of the group. They will each receive an email with a link to confirm their membership.
Once added to the group, you should see the group library in the left pane of the Zotero desktop program. Group libraries appear below your personal library. If the new group doesn't appear, try syncing manually.
You can add items and create collections in the group library just as you can with your personal "My Library." You can copy items from one library to another by dragging and dropping.
Citing items from group libraries works the same as citing items from your personal library. If your group is collaborating on a shared Google Doc, citations added to that document from the group library should work just as you would expect.
See more on groups from Zotero support.