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You can use iTunes application on your computer to download music to your iPod. First download and install iTunes on your computer --> http://www.apple.com/itunes/download/
After downloading, open the downloaded iTunesSetup file and follow the onscreen instructions to install iTunes. After installing, open iTunes application.
In iTunes, you can buy or add your music. Then connect the iPod to your computer. Select your iPod at top left. Click on Music option in left column. Enable "Sync Music" option and click Apply or Sync button. This will downlad the musics from iTunes on your computer to your iPod.
Refer this article --> https://support.apple.com/en-in/HT201253
If you have any difficulty on following the steps above, please let me know and I will continue to help you.