iCloud: Apple ID
An Apple ID gives you access to the iTunes Store, App Store, iBooks Store, Apple Online Store, iCloud, FaceTime, and other Apple services. It consists of an email address (for example, firstname.lastname@example.org) and a password. For more information about Apple ID, or to create a new one, go to the Apple ID account website.
All of your store purchases are tied to your Apple ID account, and can’t be transferred to another Apple ID account. If you made purchases on your iPad, iPhone, or other Mac, sign in using the same Apple ID to see all of your store purchases on this Mac. If an update to a store purchase is available, sign in using your Apple ID to download the update.
For more information, see the Apple Support article Use continuity to connect your Mac, iPhone, iPad, iPod touch, and Apple Watch.