Add Songs to Your Movies on Windows Movie Maker

A simple step-by-step guide on how to add music to Windows Movie Maker.

Steps

Make sure you have the music file you want saved onto your computer. Look in the related links listed below, if you don't know how to save music you want if it's on the internet or on a CD.
Open Windows Movie Maker.
Make your movie as usual (i.e. put in your pictures or clips where they need to go.)
Look to the left side of the screen. There should be a header that says "Capture Video" and below it should have an option that says "Import Audio or Music" Double click on that.
A browse box should pop up, with a list of documents. Go to where you saved your music file (preferably under "My Music" in your documents.), then double click on it or press Ctrl if you want to select multiple. It should be transferred into the Movie window with any other files you might have.
Left click and hold, to drag your music clip into the spot on your timeline where you want it to go. After positioning it on the timeline, release the left click. Your music should be where you placed it. This usually works.
From here you can crop the music (make it shorter) to fit how long your clips and/or pictures are.

Windows Movie Maker supports these types of music files: .aif, .aifc, .aiff .asf, .au, .mp2, .mp3, .mpa, .snd, .wav, and .wma Most of the music files you take are going to either be .mp3, .wav, or .wma so you don't have to worry too much about the others.
Windows Movie Maker DOES NOT support iTunes .aac and some other ones files.