Shared folders are folders in the Jottacloud sync-folder, that has been shared with other Jottacloud users. All members of a shared folder will synchronize the shared folder and it's contents, to their Jottacloud folder.
All members of a shared folder has full access to the folder. All changes done by any member, is automatically synchronized to the other members of the shared folder.
You can use this guide to learn how to share a folder.