Keep music playing when app out of focus - Android

My app runs visual scripts to play ambient music.

I want the music to keep playing when the app is out of focus.
There’s a few visual effects that can stop.

I’ve heard I need to make an android background service…but I don’t understand how.

Does anyone know where I should start ?

Beginner with C# and Android Studio.

Any help, tips, tutorials, places to start, plugins to buy appreciated.