mute a video in imovie

Q:"I want to take the volume out of my video shot around NYC today and overdub with music tracks that I made in Garageband? Is it possible that I do it in iMovie on my Mac? Or can anyone describe how to mute video on iMovie at every step? Any help would be greatly appreciated." -from MacRumors

Is there such a need for you to eliminate the sound in your captured video on your Mac and add voiceover or dub customized music track with the video like the above? On Mac, all of you can take advantage of the built-in video editor - iMovie to freely make it happen. So how does it work in practice? Below draws up a list of operation procedures of how iMovie mutes videos. More, an alternative to quiet a video is recommended to open you up to more possibilities.