To import a song, tap the Import button at the top-left of the screen.
You can import from your device’s Music Library or Video Library, or from iCloud Drive and other cloud storage services if you have the corresponding apps installed.
Songs must be physically present on the device to appear in the Music Library. If songs are missing, check the Apple Music app - if a cloud icon appears beside a song, tap it to download it to your device. Note also that some albums may appear under “Compilations” rather than “Albums”.