Music
Easy there kiddo. Adding Music is easy.
First. you need a video editing software, Now if you are a working person, you should be able to afford Hardcore programs like:
Sony Vegas:
Great tool for editing clips, You can add effects, diffrent soundtracks, Zooms, All that kind of thing. The problem with this is that it costs money, But there is a Trial, witch you can use for 30 days or so.
Windows movie maker
Now if you are a cheap bastard, you could always look for "Windows movie maker", It comes with most computer, Its basic, You can add 1 video track and 1 Sound track (I think) and then render it to whatever you want. But not Mp4 or stuff like that.