First of all, download
“MP3 Video Converter App” from Google Play Store
After you download
“MP3 Video Converter” application,
google “tubemate“
Tap the first link –
TubeMate YouTube Downloader 2.2.6 – Official Website
tubemate.net
Tap 
Tap 
Pull down the notification bar.
It says “TubeMate has been downloaded”.
Just Tap it!
Install blocked since this is unknown source. In other words, this app is not in the Google play store.
But do not worry as long as you follow my instructions.
Tap “SETTINGS“
Switch on “Unknown sources” on the bottom
Tap “OK“
Tap “INSTALL” on the bottom right
Tap “OPEN” on the bottom right
Read Terms of Use then
Tap “Agree“
Tap “Close” on the bottom
Search and play youtube video you want to download.
Tap 
around the top
Pick your Video Resolution for the whole video download, or Audio only if you want to listen to the music only, then
Tap 
around bottom left
Tap “Close“
Looking Good! It’s downloading!
Completed!
Let’s check it out!
In your “Gallery” 
there is youtube video you’ve just downloaded.
Enjoy!
To download youtube video again, you need to use TubeMate application. It’s in the app drawer 
on the home screen bottom.
Well done!