"What is two-step verification for Apple ID?
Two-step verification is an additional security feature for your Apple ID that's designed to prevent anyone from accessing or using your account, even if they know your password.
It requires you to verify your identity using one of your devices or another approved method before you can:
Sign in to My Apple ID to manage your account
Sign in to iCloud on a new device or at iCloud.com
Sign in to iMessage, Game Center, or FaceTime
Make an iTunes, iBooks, or App Store purchase from a new device
Get Apple ID related support from Apple"