There are three ways to add music.
1) One would be to plug the phone into your computer. It will show up like a hard drive with the name of the person that is named in the Parent Portal then you simply drag songs right onto it.
2) You could also get a Micro SD card, load music onto the Micro SD card, and then on the left side of the phone put that Micro SD card (in the tray with the SIM card that's already in the phone) into the phone.
3) Now, if you have the Discover plan, you can do Apple Music, Spotify, Spotify Kids, or Amazon music and download the songs right from those apps onto the phone.
Please be conscientious of the amount of hard drive space that is in the remaining on the phone especially if you choose not to use the a Micro SD card.