YouTube is of course the home of videos. And You certainly want to save some videos to your device. And to do that, you don't need to download an extra app or google search youtube downloader. You don't have to copy and paste.
The fastest way is this: edit the link and input 'pp' in front of 'youtube'. So it would be like youtubepp.com/...
And you would get a direct page to download in whatever format (audio included).