I may be over my head with this one too. Okay, I just went into my itunes player on my mac, and drug (hold mouse button down and drag and drop) a song to my desktop. Once it is there, it should have a file extension on the end. Probably either M4P or mp3. If it's mp3, I have no idea why it isn't working. If it's M4P m4a or another format, go to a site like Zamzar - Free online file conversion
and convert it to an mp3 and save it to your computer and try again.
If the song you want is only on your ipod, and not in your computer, there is another way to get it. Go to beemp3
and re-download it. If you can't find it there, go to youtube, find the song, then use this site to rip the audio and save it to your computer. 2conv
It will save it as an mp3 and then it should work. These sites are all free, and I've used beemp3 and 2conv dozens of times. They work great.