The previous page in this guide discussed the basic guidelines of fair use. If you're following these guidelines, it's generally ok to use snippets of Youtube videos for a project, provided you've found Creative Commons videos. However, keep in mind that copying and saving parts of copyrighted videos is breaking the law. And, if you're attempting to download Netflix or Amazon, those websites are definitely not supported by web tools like cpClips, since they are definitely copyright protected.
Cpclips.com is one of the many websites out there that enables you to download Youtube videos as MP4s, and you can use it on a Chromebook. Below is a tutorial: