A lot of iOS users prefer music apps like Pandora or Spotify to Apple's Music app. But sometimes you want to listen to music. Right now. And that's where the native Music app has the advantage.
To get your groove on ASAP without first searching for and opening an app, just swipe up from the home screen to open Control Center and tap the play button. Your iPhone's Music app will automatically launch and begin playing the first song available.
Note that this will not work if you have watched videos online or in an app since the last time you opened Music.