For an annual fee, iTunes Match syncs your music across all your Apple devices and offers a web-based backup in case you lose files. The service creates a single library that you share between your Mac, iPhone, iPad, and iPod touch, and when you add a song to one place, it automatically appears in the others. Here's how to turn on iTunes Match and use the service.
Apple — How do I set up iTunes Match?
To install iTunes Match on your computer, use the iTunes Store.
Scroll to the bottom of the screen and select iTunes Match.
On the next screen, select Subscribe.
