Transfer whole bookmark lists between two PCs
Bookmarks are stored in files with the extension *.wsw, downloaded files in the related subdirectory *_WSW. If your bookmark file has the filename bookmarks.wsw, then all downloaded files are stored in the related folder bookmarks_WSW.
To transfer all bookmarks between 2 PCs, you have to backup that file inclusive related subdirectory and restore the backup on your second PC. Bookmark files can be opened with File+Open.
You can also use the Integrated backup feature to backup/restore bookmarks to/from a ZIP archive.
To keep two existing files in sync, you can use the Synchronization feature.