
You need to be signed in using the same Apple ID on all your devices to use iCloud to sync data and services across all of them.

On Apple devices: You can login to iCloud on an iPhone, iPad, Mac, or Apple TV.You can change your Apple ID and manage your account using the Apple ID account website. It’s really important to protect that information, which is why your Apple ID should be protected with a complex alphanumeric passcode you can remember (and must also be protected by two-factor authentication). When you sign into a device with your Apple ID, you also sign into iCloud. Your Apple ID is the key to iCloud and all Apple’s services. Underpinning all of this is your Apple ID and iCloud login. Third-party developers also use iCloud, thanks to Apple’s CloudKit framework and tools they use to build apps that sync across devices. When you are logged into iCloud on a device using your Apple ID, (and this includes some non-Apple devices when using specific iCloud-supported apps or services, such as Music), you can access some or all these services. ICloud login is the key to this part of the Apple Garden. Look and you’ll find 65 services listed there. These include many you may never have heard of before, some you may not use, and a variety of services you may already rely on at work, such as the Device Enrollment and Volume Purchase programs. The iCloud System Status page is the best way to understand the extent to which iCloud supports Apple’s ecosystem.
