Latest iPod requires latest iTunes, i.e version 12. iTunes 12 requires Mac OS X 10.7 Lion or later. The latest version of OS X is 10.10 Yosemite --> http://www.apple.com/osx/
If you are using 10.6.8 Snow Leopard, then you can download and install 10.10 Yosemite from App Store for free. Go to Applications folder and open App Store. Search Yosemite or select Yosemite and download/install it. It is a 6GB file, so it would take a few hours to download and install it.
Once Yosemite is installed, you will get latest iTunes and you will be able to use your iPod.
If you are using 10.5 or lower version of OS X, then you have to purchase and install Mac OS X 10.6 Snow Leopard first. You have to buy the Snow Leopard discs and you can buy it from here --> http://www.apple.com/shop/product/MC573Z/A/mac-os-x-106-snow-leopard
Upgrading to Snow Leopard is easy. When you get the discs, just put it on your Mac and follow the onscreen instructions to upgrade. After upgrading to 10.6 Snow Leopard, you can download and install Yosemite for free from App Store.
Upgrading won't delete any of your files, but backup your important files before upgrading the OS X.
If you have any questions or would like any additional information, please don't hesitate to ask.
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