If you have an iPod, iPhone, or iPad, you can take your iTunes library with you wherever you go. You can take your whole library or only certain items—songs, movies, books, podcasts, photos, and so on. You can also add contacts, calendars, web bookmarks, mail accounts, and notes.
You can use iTunes to set up, manage, and add content to your iPod, iPhone, or iPad. Adding items to your device is called syncing.
You can sync iPod touch, iPhone, and iPad with only one iTunes library at a time. You can sync other iPod models (besides iPod touch) with multiple iTunes libraries by choosing manual syncing.
If you subscribe to iTunes Match, you can’t use iTunes to sync music to your iOS device, but you can sync other types of content. For information about adding music to your device from iCloud, see the the documentation for your device.