Editing my Gatorade Commercial

I have completed the filming process of my Gatorade commercial, now it is time to edit my commercial. I have dumped all of my film on to my laptop, and imported it into imovie. I during this process I had to add music and edit the film so the commercial would make sense. I first put all of the clips in order of how I want them to be shown in the commercial. I had to edit a few clips to make sure that the clips would be able to make sense. A problem I ran into while editing the clips was timing since the commercial had to be thirty seconds, I added some clips to the commercial. I also had issues with sound, since there was noise in the background of my scenes. At first I didn't know what to do about the sound in to background of my scenes, however I learned that I could turn down the sound of the video clips. However this brought about a new challenge when editing my commercial. The new challenge is that I wasn't able to add any music or sound to the scenes of my commercial. ...