My songs on my iphone did not show on my google play music app

So i want to use google play music as my main music app on my iphone 6s because it offers chromecast streaming. However, when i downloaded it, my songs on my phone did not show on my google play music app. Why? What do i need to do?

The phone app is a player. The computer app is the one that loads the music. I have all my music in iTunes on my computer, Google Play Music uploads it so it can be played on all my devices. It works really well.

So, you need to sync the music on your phone with your computer. Not a bad idea to have a backup anyway.