Using sound for both sync and non-sync purposes is an important aspect on non-linear video editing. In this way you can use the sound from one clip on another, over lap sound from different places, make the sound out of sync for the associated video for effect, or just make the decision to use the sound from a video clip. This is difficult in the Windows Movie Maker Timeline because of the way the developers have focused on ease of use over functionality. Instead of just having the ability to move around the blocks of sound independent of the video the two end up being one consistent unit. There is a way to approach this in Windows Movie Maker if you want to end up just using the audio from a video clip over other video clips.
When you are editing clips in the Windows Movie Maker Timeline each clip will stack after each other according to the order that they were added to the Timeline. From here each clip will occupy the Video track and the Audio track. Once you are editing you may end up realizing that you want one clip just for the audio and would like to move that audio clip independent of the video. If this is the case select the Audio track portion of that video audio pair and drag it from the primary Audio track down to the secondary Audio / Music track. This will transform this clip from a video audio pair to just the audio and will move around as a secondary audio or music clip.
Changing Clip Position
This clip will then give up its position in the sequence and all the subsequent clips will realign themselves according to the previous clips absence. In this way this method is also a technique for moving the video clip from its position in a sequence to the end of the sequence. You can drag the clip down to the secondary audio track and then move it to the end of the sequence. If you drag it back up to the primary Audio track the video will return and the video audio pair will be restored.