Update Music Folder? Read by iTunes

Newbie to MP3Tag. I opened my "Music" folder in MP3Tag and edited a number of files, learning as I go.

Question: Is the music file automatically updated with MP3Tag or do I have to save the file as Music or another name?

Depends.
Editing in the files list usually writes the modification to the file as soon as you leave a single field.
Editing in the tag panel usually has to triggered explicidly either by Ctrl-S or with the Save function from the toolbar.
This describes the behaviour on delivery and first time installation.

You can adapt the settings in the Tools>Options dialogue.

I thought that was process. question I have is I have processed dupes out of iTunes with "DupeLiminator". Music and video counts is 12,517 in itunes, but MP3Tag shows a file count of 21,500. ANy idea what extra files could be?

No.
I cannot judge what that Dupeliminator does - if it e.g. does not really delete files physically but only from the database.
What happens, if you re-read the Music folder with iTunes? Does that restore the duplicate files?

A list of included file extensions for MP3tag can be seen in Tools>Options>Tags.

Dupe Eliminator moves files from Music file and writes the deleted files to a separate folder called "deleted"

If I re-read Music file in iTunes, dupes are gone.

Is there a method to write the MP3Tag file I edit to a new file or a spreadsheet where I can edit the file for dupes or anomalies?

Appreciate the help.

You can use an export script to create csv-files that can be read by e.g. Excel.
MP3tag has no built-in method to detect duplicates.
Does MP3tag also read the "deleted" folder? This would explain the higher number of files.