An Apple ID gives you access to the iTunes Store, App Store, iBooks Store, iCloud, FaceTime, and other Apple services. It consists of an email address (for example, email@example.com) and a password.
Note: In some locations, you can use a phone number instead of an email address as your Apple ID.
All of your purchases are tied to your Apple ID, and can’t be transferred to another Apple ID. If you make purchases on your iPad, iPhone, or another Mac, always sign in using the same Apple ID so you can see all of your store purchases on this Mac and download any available updates.
For more information, see the Apple Support article Use continuity to connect your Mac, iPhone, iPad, iPod touch, and Apple Watch.