How can I put videos that I have on my desktop from my digital camera, into my itouch?

I have videos that I have taken on a digital camera which are now on my desktop and I want to have on my itouch. I think I have to put them into some sort of format before i can place them into the ipod, but I don’t know how to go about this. is there anything I need to download?... or is this simply not possible. thank you for any help you can provide