There are a few methods to create collections with Librarian Sync.
- [/mnt/us/]extensions/collections.json: regex based on path and filenames, can have multiple collections per book
- folders: based purely on folder hierarchy, one collection per book
- [/mnt/us/]system/collections.json: generated by the Kindle Collections plugin for Calibre, can have multiple collections per book
Note: system is a hidden system folder
Not sure how LS handles magazines. The Kindle I use with LS is unregistered as I prefer to keep my "normal" books separate from fics.