It depends on what music you are looking for in Amazon.
First, Amazon offers 2 music plans: Prime Music and Amazon Music Unlimited. However, you must pay the subscription fee to enjoy these music services. If you are Amazon Prime member, then you can enjoy Amazon Prime Music for free.
Both music services offer 30-day free trial, if you are not sure which one to choose, you can try them first before you decide.
Second, you can download free music from Amazon. Go to Amazon's Free Digital Music page, and you will see a list of free songs from all genres. You can select the songs you like and download them as MP3 songs.
Important Note: Some of the free music is marked as "Prime". If you see this kind of music, it means the song is free only to the Amazon Prime member.