YouTube is not only the biggest library of videos, it is also a huge resource to find your favorite songs. At desktop computers it is possible to play Youtube music in the background while working on other tasks. On Apples iOS devices (iPhone, iPad, iPod touch) the playback of Youtube videos in the background requires a littel workaround.
Do not use the Youtube app but open the Safari browser on your iOS device and play any of your favorite song on YouTube. Once the music started, tap on the Home button to switch to the home screen. The music playback will stop.
Now swipe up with on finger from the bottom of the screen. This gesture will open the Control Center. Now tap the Play button and the paused YouTube video playback will resume. Now you can switch to any app on your iOS device and the audio stream from Youtube will continue in the background.