What is Apple ID?

Your Apple ID (now shown as your Apple Account) is the account behind everything Apple: the App Store, iCloud, iMessage, FaceTime, subscriptions and purchases. One account signs in across all your Apple devices.

Manage it from Settings → [your name] — payment methods, security settings, trusted devices and family sharing all live there. Protect it with two-factor authentication; losing an Apple ID means losing purchases and iCloud data.