I went thru a learning curve with google music. But I love it. Have the family plan. Step 1. Go to settings scroll down. Go to storage location. Click external, you should see the ad card you installed.
2. This was one of my mistakes when I reset my phone and wanted to re download my phone. Create a custom playlist. If you have to reset your phone, all your music as long as it is in your playlist will download automatically or download when you click the icon download.
3. Once you have a playlist. Download it. There's a greyed out circle with an arrow in it, in the playlist.
4. Once you have it downloaded. To test go back to the menu (the menu is the 3 lines in the top left). Check download tab.
5. Go back to menu. Then playlists. If you did it correctly. You should see an orange circle with a checkmark in it. That means you can now play the music which has been downloaded to your phone and it is not being streamed.
Also. If you have your music in different playlists. You should go to songs. Btw. This needs to be done from a pc. Click the first song, hold the alt or ctrl button and go to the bottom. Then, you can move all your music to one playlist. The reason why you want it all on one playlist is for reset options only.
If you reset your phone, you will have to download all songs again individually, which I did a few times. PIA.
If you need more help plz respond and maybe we can text or something with pics of the software. Like I said it can be a learning curve. I'm teaching my wife now as she came from apple. But once you get it and do it. It is simple.