General help required

I am once again very confused by all things Apple!

Issue 1

I opened my iTunes today to find it has made duplicates of all my songs. Why does it do this and how do I prevent this happening again (this isn't the first time!)? I am currently manually deleting the duplicates which is taking hours.

This leads me to my next question ...

Issue 2

I have an album on my iPod (iPod touch 5th generation I think) but it is not in my iTunes library .... how do I get it from my iPod into my iTunes library. I am wary of 'syncing' as I think this causes issue 1 above!

TIA