Help with cover art on I Pod Touch?

so I really need help with my I Pod touch, it first started when I had my I Pod hooked up to my computer and there was this bar at the bottom of my I Pods library that is "AutoFill" and when I pushed it, it made copies of some songs, which I deleted and I was like whatever, that was stupid. But later when I went to go listen to music, the cover art for about half of my songs had been replaced with the cover art from one of my songs, confusing, i know. But the cover art that replaced the REAL cover art is the cover art from my MOULIN ROUGE! album, so now when I listen to " Marry you" for example, instead of seeing the cover art for Doo-Wops & Hooligans, I see the MOULIN ROUGE! cover art. I was just going to go on my computer and replace the cover art, but when I went to my I Pod's library on my computer, I left clicked on the song with the wrong cover art and clicked "see info" and went to the cover art section, but it won't let me click on anything, and it show the right cover art on THERE but it doesn't on my actual I Pod. Another problem is, I bought alot of songs on I tunes using my actual I Pod touch instead of on my computer, but when I connect my Ipod to my computer, all that purchased material doesn't import into my primary library. I tried syncing it, but nothing happened. I'm getting another I Pod for christmas, and I want to be able to put all those songs I bought on it, but I can't if they won't go into my library. Please help! Sorry this was so long but I'm an idiot when it comes to technology.