New Device

• if all the music on your old iPod is from the iTunes Store, and you downloaded it directly from the store to your iPod, sign into your account on the new iPod and download the music from the store
• if any of the music on your iPod was copied (not transferred) from your iTunes Library (on your computer) to the iPod, you use the same procedure to copy it to the new iPod: connect the iPod to your computer and once iTunes sees the iPod, set up options to Sync between iTunes and the iPod. If you don't know how to do that, see Sync your iPhone, iPad, or iPod using your computer - Apple Support . If you're still stuck, post back here.

You will have noticed that I said "copied, not transferred".

• If you were to transfer your music from one iTunes/your computer to an iPod, it will no longer be on the computer when you next need it (such as now). Not only that, but it's then possible to fall into the mistaken belief that you can then delete any copy of that music that you find on your computer (please don't!)
• If you copy the music from iTunes to your iPod, your iTunes can still manage your music and it will be available for copying to your next device. In addition, you will have a backup of your music for the time when your iPod fails, gets broken or gets stolen

Make sure though, to make a backup of the music that is on your computer; an iPod is not a suitable location to back up the computer.