Gather all the various elements that you'll be working with in the collections pane: video clips, background music, sound-effect files and narrative. You should already have these files located on your hard drive. Move them into a single folder. This way, they'll be much easier to find when you need them.
Open Windows Movie Maker and click "New Project" in the "File" menu.
Click "Import Media" and navigate to the folder where all your elements for this movie project are stored.
Import the contents of an entire folder by clicking "Ctrl+C" to highlight all files, then click "Open." This saves you time by not having to import the files one by one.
Select your video clips that you wish to work with and drag them into the timeline bar (located at the bottom half of the screen.) Arrange the order in which you want the clips to appear by dragging them into place.
Drag the first audio file you wish to mix in from your collections pane into the timeline. Continue adding audio files until all the sound tracks have been set into place. Just as with video clips, you can reorder and trim audio files.
Adjust the volume of each individual audio clip by clicking the "Clip" menu, then select "Audio," then "Volume." Slide the volume level slider to the left to reduce the sound level; move the slider to the right to increase volume.
To mute the selected audio, select the "Mute" check box. (This is helpful for portions of your movie where you wish to use narration or the original sound from your video.) To reset the original volume levels, click "Reset."
Add a voice narration track to your movie by inserting the cursor at the point in your timeline where you want the narration to begin. Press the “Narrate Timeline” button located to the left of the timeline. The narration wizard will pop up. Select your microphone input as the recording device, then press "Record." The narration wizard plays your video while you're recording your voice track to guide you.
When you are done recording the narrative, press "Stop." The narration track will be automatically inserted at the point specified in your timeline.
Play back the newly mixed movie in the preview pane and listen carefully. Are all the various elements proportionate to one another? Is the music too loud? Does it compete against the narration or video sounds? To make adjustments, click the "Tools" menu, and then "Audio Levels."
To increase the level of audio from your video clip source, drag the slider toward "Audio from Video." To increase the level of audio that is on the narration/music track, drag the slider toward "Audio/Music." Then click "Close."
Fade audio tracks in or out by selecting the audio or video clip on your timeline that you wish to apply fade effects to. Go to the "Clip" menu, choose "Audio," and then click either "Fade In" or "Fade Out."