On iPhone 5s, you can use a fingerprint instead of your passcode or Apple ID password to unlock iPhone or make purchases on the iTunes Store, App Store, and iBooks Store.
Set up the Touch ID sensor. Go to Settings > Touch ID & Passcode. Set whether you want to use a fingerprint to unlock iPhone, and to make iTunes Store, App Store, or iBooks Store purchases. Tap Add a Fingerprint and follow the onscreen instructions. You can add more than one fingerprint (your thumb and forefinger, for example, or one for your spouse).
Delete a fingerprint. Tap the fingerprint, then tap Delete Fingerprint. If you have more than one fingerprint, touch the Home button to find out which fingerprint it is.
Name a fingerprint. Tap the fingerprint, then enter a name, such as “Thumb.”
Use the Touch ID sensor to unlock iPhone or make a purchase. Touch the Home button with a finger you’ve added in Settings. You can unlock iPhone from either the Lock screen or the Passcode screen. When purchasing from the iTunes Store, App Store, or iBooks Store, follow the prompts to enable purchases with your fingerprint. Or go to Settings > Touch ID & Passcode and turn on iTunes & App Store.
Note: If you turn iPhone off, you’ll be asked to confirm your passcode when you turn iPhone back on and unlock it the first time, and you’ll be asked for your Apple ID password for the first purchase you make.