In the left column of this page is a video tutorial and in the right column is some text about group libraries
If you need to have a group folder with shared highlighting and annotations there are a couple of ways this can be accomplished. Basically, any markup on a PDF that is shared within Zotero should show that markup to other group members. One free tool for doing this on your desktop is Foxit. The iPad and Mac app Papership has a pro version that allows for markup as well.
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.
First, set up Zotero sync and synchronize your library.
This is what the "Create Groups" button should look like
Once you create a group library and sync your Zotero software, you will 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.
Search for existing public groups or create a new group. Groups may be public (searchable, and anyone can join) or private (users can only join if invited).