Open the iTunes Store app or the Music app on your device
Sign in with your Apple ID
Search for the song, album, or artist you want to buy
Select the item you want to purchase
Tap or click the price button
Confirm the purchase with your Apple ID password, Face ID, Touch ID, or device passcode
Wait for the download to complete if it does not start automatically
Check your Library or Purchased section to find the music
Repeat the steps for any additional music you want to buy