create folder in iTunes music

Typically you would use the default preferences for Keep & Copy that are found under Edit > Preferences > Advanced so that anything you add to the library is organized where iTunes would normally place it within the iTunes Media folder. You can use File > Add Folder to Library to import an existing folder of content, or copy files that you want to add to iTunes into the Automatically Add it iTunes folder which is inside the iTunes Media folder.

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See Sync your iPhone, iPad, or iPod using iTunes on your computer - Apple Support.

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