Syncing libraries
Libraries in your desktop Zotero program, Zotero Web Library and your iPad Zotero can be synchronized, so that all references, attachments and notes are the same regardless of where you open the library concerned.
To synchronise go to the desktop program and click Edit - Settings - Sync -
Fill in your username and password and click Set up Syncing:
After that choose your preferences
You can click Choose Libraries to select the libraries you want to synchronise.
Sharing libraries
You can manage who you want to share this library by going to https://www.zotero.org/groups and click Manage Members to invite new members
Click Send More Invitations and fill in the emailaddress(es) and click Invite Members
The new invited member will receive an email with a link to the group and can accept or decline the invitation and has to log in or register to join this group.