Apple Resources - Apple ID

Apple ID Support
  An Apple ID is the account you use to access Apple services
  like iCloud, the App Store, the iTunes Store, Apple Music,
  and more. It includes the email address and password that
  you use to sign in, and all the contact, payment, and
  security details that you'll use across Apple services.

  No matter where you create your Apple ID, just remember to
  use the same one to sign in to every Apple service. That
  way, you can access and manage everything with a single
  account and password.

Multiple Apple IDs just leads to multiple problems

Reset (Forgotten) Apple ID Password Reset (Forgotten) macOS Computer Password Boot (Command-R) > Utilities > Terminal, type: resetpassword Reset (Forgotten) passcode for your iPhone, iPad, or iPod-touch Contacting Apple 800-MY-APPLE (800-692-7753) Find My (all your Apple devices using the same Apple ID) Demo Find My iPhone (or iPad, iPod or Mac)

iCloud & iCloud Drive iCloud mostly serves to back up your device and sync limited kinds of data to other Apple devices, while iCloud Drive more focuses on sharing among devices and seamless interaction and co-working among devices, which means that data in one device can be shared among other devices without copying, sending or transferring. For example, you create a new Pages file on your MacBook Air, put a few lines on it, and then throw it into iCloud Drive. Then you may continue working on it wherever you go as long as you have access to it via your iPhone or iPad. What does iCloud back up? iCloud Security E2EE (End-to-end encrypted data) End-to-end encryption provides the highest level of data security. On each of your devices, the data that you store in iCloud and that's associated with your Apple ID is protected with a key derived from information unique to that device, combined with your device passcode which only you know. No one else, not even Apple, can access end-to-end encrypted information. Access and manage files in your iCloud Drive