Best way to download videos off of YouTube and embed them on a PowerPoint?

I’m doing a presentation for school next week, and I want to have some videos on my powerpoint.
The videos I want are on YouTube, and I can tell you I’ve used pretty much every “YouTube Downloader” there is and none of them seem to work.
So, what’s the easiest, most reliable way you’ve found to download YouTube videos?
My second problem is that I haven’t had experience embedding videos on a Powerpoint, so, any ideas for that too?