iTunes won't load my music files
On MacBook Air (OS X 11.6, which isn't listed on the Communities page), I follow the instructions for loading downloaded music files into my iTunes Library ("1. Drag a file or folder from the desktop to the iTunes window"; OR "2. In iTunes, choose File > Add to Library or Add Folder to Library, locate a file or folder, then click Open"), and ... nothing happens! The files in question are FLAC music files. I've tried this dozens of times. What am I doing wrong? Thanks!
MacBook Air, iOS 11.4.1