Unfortunately Apple doesn't make it easy to use iPods, iPhones, and iPads with Linux. In fact, strangely, Apple makes it far easier to use these devices on Windows than on Linux, which is odd given the underlying systems of Linux and OS X are based on the same Unix model.
Whatever the reason, the fact is that there is no iTunes version for Linux.
The Linux application that should be able to put music onto your iPod is called gtkPod, which you can install via the Add/Remove application available from the Activities Overview.
To access the Activities Overview, move your mouse into the top left corner of your screen. Once the Activities Overview dashboard appears, start typing Add and the Add/Remove Software application should appear in your search results.
Launch Add/Remove Software. Once it's open, do a search for gtkpod. Install the gutenprint driver packages.
After it installs, launch gtkpod and load up your iPod. GtkPod features a robust conversion system, so you might find that even music that wouldn't have normally worked on your iPod will now be automatically converted into an iPod-compatible format.
Remember the issues with "bricked" iPhones? It seems Apple frequently makes changes in the programming of the devices without telling anyone, resulting in sudden incompatibilies. If you're using and iDevice with Linux, don't update the iDevice too often, if possible, until you read online that its a "safe" update.
The fact that you bought a music player should not control your choice in computers that you use. If you own an iDevice, send Apple feedback at apple.com/feedback, ConsumerAffairs.com and Better Business Bureau requesting for better support. Apple needn't expend their own time and effort on Linux support; they need only to make it known what they are changing so that the independent Linux programmers know what to change!
And finally, vote with your wallet. If Apple doesn't want you to have a choice of computing platform as long as you have an iDevice, simply stop purchasing iDevices. Look around, try other devices (many of them run Linux) and you're sure to find a similar device that is a lot more open.