From Apple’s iOS 9 preview page:

It securely transfers your contacts, message history, camera photos and videos, web bookmarks, mail accounts, calendars, wallpaper, and DRM-free songs and books. And it will help you rebuild your app library, too. Any free apps you used — like Facebook and Twitter — are suggested for download from the App Store. And your paid apps are added to your iTunes Wish List.

It’s like migration assistant for Android to iPhone switchers.