The video below is an example of using a an audio track that includes your own narrative plus music with sounds recorded by the camcorder in the background too. The directions to do this are below the video.
To add a narrative it's best to use a microphone instead of the speakers that come with your computer. The vocal quality will be much better. I used a Logitech microphone that plugs into a USB port. When you plug it in the computer automatically processed the software to use it.
In Windows Movie Maker 6.0 click on "Tools" in the menu across the top and choose "Narrate Timeline." With your video showing in the timeline, click to start playing it, click "Start Narration" and begin talking. Be sure the microphone button is turned on. When you are done click "Stop Narration."
You can start the narration at special points along the timeline. Between narration clips you can also add music clips. Below this you can add text also that shows on top of the video.
The text on top of the clips might be useful if someone is viewing the video without the sound turned on if the computer is in a library, public place or classroom.
To make the video I used a Canon FS100 camcorder with 48X zoom that I bought a year ago.

