How to delete or remove duplicate files from Mac not just itunes

I'm in school and have been given many old files and a lot of them are repetitive I was wondering if there is any software that can clean up and remove all the duplicate files. If I could use it for the duplicate itunes that I have that would be great too.

Oh and I'd prefer it to be a free and easy to use program. Or at least have some easy to understand how-to instructions. Oh and P.S. I'm new to mac so some things may need to be dumbed down or be forgiving when I have to ask questions. Thanks for understanding we were all there once.