Vocals + Vid.......

Hey all,
So im starting to record songs using garage band. But i want to start posting things on youtube. So my question is.....
How will I do so on a mac? Is there any extra stuff im going to have to buy??
So when i record this, I want my webcam/vid cam to be filming it so all can see me and i also want the vocals/backing track to be herd clear like alot of the other youtube cover songs have. when i record it, I can never get the backing track to be herd loud, you can only hear me singing.
I just a new way to record this so it all works fine.....
Thanks in advance.....

Record the music in GarageBand, export it to iTunes, record the video, and then in iMovie add the song as soundtrack, or sound effects, or whatever it is. That's the only way I can think of to do it.
Then you can upload from iMovie directly to YouTube.