How do I put a song on my youtube video?

mmk it's a miracle that I even got the video up. I would like to put requiem for a dream on the video. When I go to edit video, and then click audio, I search for that song and can't find it. It is a football highlights video so I thin it sounds good with it...plus the video is 20 min long so I figure instrumental would be best. I guess I can't can I? I mean when I go to search for it...nothing comes up! If you can help me, please give details.