What's the difference between Media Library and Database?

Problem:

All my new MP3 files are in a folder named X. I use MusicBrainz tagger to tag them. After tagging, MusicBrainz moves each file to its own folder. ( F:\Muziek\*first letter artist*\*artist*\*album\ )

My Media Library Music Folder is 'F:\Muziek\'. As far as i know, executing 'Rescan Media Library' causes Foobar to search in 'F:\Muziek\' for new mp3 files who have not been added to the library playlist.

Anyways, when i run 'Rescan Media Library' I can't find my new files in my library playlist (nor with Ctrl-F), although I CAN find them by using 'Database Search'.

What am I doing wrong, or misunderstanding?

"Rescan Media Library" just adds the files to the media library, but not to any playlist (unless you have an autoplaylist).