windows movie maker only accepts MPG, MPEG, AVI , M1V , and MP2 files . Pretty much it only accepts microsoft based applications. If its run through Apple Quick Time or any other media application it wont work.
If it is one of the accepted formats all you have to do is open Movie Maker and click on Import Video , select the location where the video is stored . It will then show up in Icon form to the right in your “collection” . Just drag it from here into your story board and that’s it . You can cut , overlap and change sounds all there . Just play around with it , its pretty simple to use