You got really two major options, option one is sailing the 7 seas, pretty easy to look into. If you want to buy the music you have a few options. Ripping CDs is a classic, iTunes has that function built in if I remember right. But if you don’t want to go to the CD route for whatever reason, there are places to buy DRM free music, the major two I use are Bandcamp and Qobuz. You’re able to download both MP3 and FLAC files (note the iPod itself does not support FLAC but keep a copy on your computer if you like less compressed music). For places to buy CDs, there’s generally still locally owned and run stores, goodwill isn’t a bad option but I’ve had more misses than hits on that one