It's not that you should put it in disk mode...it's possible that you may have done this by accident.
When you are plugged into your computer and iTunes is showing the iPod on the screen, go to tab that has the iPod pictured and un-check the "enable disk mode" box.
Also, my recommedation as a newbie to iPods would be to make sure the auto sync option is checked and to always read any pop-ups that come up when syncing the iPod so you know exacttly what's going on...sometimes it might be asking if you want to erase everything on the iPod...if you don't read it and simply click yes, you lose whatever is on there.
It's all pretty simple once you are up and running.
Go to the help section above for more...there's a lot of good advice there.
iPhone 4S 64gb
// SOL Republic Tracks HD
// iPad2 64 gb wifi
// Apple TV 3 //