Windows (Live) Movie Maker is a rather limited video editing program that works on computers running Windows 7 or later. Windows Live movie Maker is a free program so if your Windows (7 or 8 or 10) computer does not have it then you can download it free from the internet (you may need to search for ‘Windows Live’).
The biggest problem with Movie Maker is the lack of a proper 'timeline' which normally would make it easy to trim clips, to scrub through the video and to see exactly what is happening at specific times. Movie Maker has a limited kind of timeline in the right panel - you can make it slightly more useful by expanding (zooming) the timeline to use more of the panel. A much better video editor is Sony Vegas but this is not free. It's worth mentioning that there is a free program that can do video editing tricks that Movie Maker is unable to do. It's called... Blender!
Video is not a moving image, it is a sequence of still images, but since your eye sees so many still mages every second (25 images every second on European TV) your eye gets the impression that it is looking at a moving image. Since video consists of a large number of still images, video files are very large. This is a problem if you have to work over a slow school network, for it means that the video may not play smoothly.
These are the skills that you will learn as you work with me on Movie Maker for a couple of lessons: