The email address you use to access many Apple resources, such as the Apple Online Store, the iTunes Store, the App Store, the Mac App Store, and also iCloud features. If you’ve purchased products from any online Apple locations, or if you’ve turned on iCloud on any devices with iOS 5 or later installed, then you have an Apple ID.
If you already have an Apple ID, you should use the same email and password to set up iCloud on each of your iOS devices and computers.
To see which Apple ID you use with iCloud, do any of the following:
On your iOS device, go to Settings > iCloud.
On your Mac, choose Apple Menu > System Preferences, then click iCloud.
On your Windows computer with Windows 8, go to the Start screen, then click the iCloud tile.
On your Windows 7 computer, choose Start menu > All Programs > iCloud > iCloud.