YouTube Premium
If you have a YouTube Premium subscription, download YouTube videos from the official YouTube app. This requires a paid subscription, but there is a trial and it comes with other features beyond the ability to save videos. To save a video from YouTube to your Android, launch the YouTube app, find the video you want to download, then tap Download below the video and choose quality options, such as 720p or 360p.
TubeMate YouTube Downloader
TubeMate is a free third-party app that downloads videos from YouTube, Vimeo, Dailymotion, and other video streaming services.
Y25s Downloader for YouTube
Y25s is a website that downloads videos from YouTube to your computer, after which you can transfer the files to your Android device. Another way to use Y25s is from your Android phone or tablet, using a web browser such as Chrome or Firefox.