When someone shares a Lightbox or Project with another Mediagraph member, they will get a notification and the Project will appear in their "Shared with me" Lightbox Organizer.
This is where notifications appear. Click the notification icon to mark it as read.
This is where shared Projects and Lightboxes first appear.
You can move Lightboxes and Projects out of the Shared Organizer if you want them to live in the main part of the Projects Panel. Simply click the pencil to enter rearrange mode and then drag the it to the main part of the Projects Panel.