To create a game video, you will need to follow three steps.
Edit your game footage. You will want to select the parts of your game footage that match the script you will follow when presenting the game in class. This will mean cutting and combining the relevant parts of your video. You may use the video editing software of your choice. For editing simple videos under Windows, Movie Maker is unfortunately no longer available, but the Windows 10 version of Photos includes video editing capability. For Mac users, iMovie is free and powerful.
Compress your video. Videos exported from video editing tools are usually far too large to work with. You can compress your video using the free Handbrake tool. Select MP4 video format.