Your Apple ID is the account you use to access Apple Services like the App Store, Apple Music, iCloud, FaceTime, the iTunes Store, and more.
An Apple ID consists of an email address and a password. In some locations, you can use a phone number instead of an email address. See the Apple Support article Use your mobile phone number as your Apple ID.
Sign in with the same Apple ID to use any Apple service, on any device. That way, when you make purchases or download items on one device, the same items are available on your other devices. Your purchases are tied to your Apple ID, and can’t be transferred to another Apple ID.
It’s best to have your own Apple ID and not share it. If you’re part of a family group, you can use Family Sharing to share purchases between family members—without having to share an Apple ID.