im assuming youre using a Mac to sync the nano, right? if youre on Windows you can still download iTunes, just a warning, download it from Apple's website rather than the Microsoft Store as the MS Store version doesn't install the drivers to support syncing iPods. If you're on Windows let me know and I'll break that down for you.
Mac method as below:
the iTunes Store still exists, just is hidden in the Music app. to make it visible in Music's sidebar:
Open the Music app
go to the settings (found under "Music" in the Menu Bar, or you can use the keyboard shortcut "Command-,")
General > tick the box "iTunes Store"
click OK
if you don't already have any music youve purchased through iTunes you'll have to buy some, since (haha I learned this the hard way as I was very late to the iPod party) you can't sync songs you've added to your Apple Music subscription Library since you don't actually own those files. if you have purchased from iTunes before but can't see your purchases on your Mac refer to this article: 120552
now, I couldn't find an Apple Support article on syncing older non-touch iPods so just pretend the article I linked below says nano rather than touch, the method is exactly the same. Just ignore the Wi-Fi syncing section, as that's obviously not possible on such a Wi-Fi-less device haha.
Article link: ios
Syncing also works through the Music app in basically the same way as described in the article above for syncing in Finder. I've often found that either Finder or Music will refuse to eject the iPod and I'll have to use the other app, so it's good to have options. Although, as I've also found, you'll probably have to sync the iPod through Finder the first time after a Restore or using a different computer (so, this won't apply if you haven't Restored the iPod prior, or have used the intended computer to sync the iPod before).
happy iPodding
and let me know if you need anymore help or if youd like me to explain more or rephrase etc
:)