Android : Unsure about structure for music app

I'm trying to build a Music Player using a service just to learn how it works.

I have two questions :)

First is I'm pretty unsure wethere to display notification to user when activity still is visibile or when they close the activity onDestroy to show which song is still playing in background...

Second is if it is correct to start service immediately as song start or should I send it to continue when activity closes and then invoke service? Right now I have music player in service and every action by user as paus, play etc goes to service to handle on a own thread...

I know how to use the components, only unsure in which order :/

/Thanks!