iTunes Help

Can someone please try to help me out here. Either I am completely stupid or the iTunes help guides are not aimed at people who are using iTunes for the first time.

I am trying to import a TV programme in avi from my computer to my iTunes library. I have tried the drag and drop function as well as the File>"add to library" route, but it has not worked, as I cannot see anything in my library.

Could someone please tell me if I am doing something wrong or how I can do this in a way that will actually work?

Thanks in advance.

 

I wanted to ask about my iPod?

When you do Sycn it to iTunes and it copies music over to it it works for me.

But say you have added more music to your iTunes and you come back with your iPod and sync it again will it just copy over just the new music or will it keep making dabble of everything on the iPod