: Authenticate with Face ID , Touch ID , or your Apple ID password to complete the transaction.
: Once bought, the song will automatically download. You can find and play all your purchased tracks in the Apple Music app under Library > Downloaded . Managing Your Purchases
: You can manage your billing info or add Apple Gift Cards directly through your Apple ID Account Settings.
Buying songs on your iPhone is a straightforward process through the app, which remains the primary way to own music permanently rather than just streaming it. How to Buy Songs on Your iPhone