- Connect the iPod to the computer and transfer iTunes purchases:
iTunes Store: Transferring purchases from your iOS device or iPod to a computer
- Transfer other music by using a third-party program like one of those discussed here:
Copy music
- Connect the iPod to the computer and make a backup by right clicking on the iPod under Devices in iTunes and select Back Up
- Restore the iPod from that backup
Note that the iPod backup that iTunes makes does not included synced media like apps and music.
Then see:
How to use multiple iPods, iPads, or iPhones with one computer
What is the best way to manage multiple...: Apple Support Communities