From the iPhone 5S onward Apple have given their handsets extra security, by featuring a fingerprint sensor. Here is how you can set this up, if you haven't already done so.
Setting up Touch ID
Step 1 Go to Settings
Step 2 Select Touch ID & Passcode and turn Passcode 'On'
Step 3 Enter and then re-enter a four-digit passcode
Step 4 Set iPhone unlock to 'On'
Step 5 Tap to 'Add Fingerprint'
Step 6 Follow the instructions and place the thumb or finger you use most onto the home button
Step 7 Adjust your grip and continue to place your thumb/finger on the sensor, for as long as you can feel small vibrations.
You can add more than one fingerprint if you sometimes use different fingers.
After setting up Touch ID you can use it to unlock your device or make purchases in the iTunes Store, App Store and iBooks Store.
Unlock your device using Touch ID
Step 1 Press the Home button or the Sleep/Wake button to wake your device
Step 2 Lightly touch your finger on the Home button to unlock.
If you reach the passcode-entry screen accidentally, you can still use Touch ID to unlock your device.
Make purchases with Touch ID
Step 1 Make sure iTunes & App Store is turned on under Settings > Touch ID & Passcode. If you can't turn it on, you might need to sign in with your Apple ID in Settings > iTunes & App Store.
Step 2 Open the iTunes Store, App Store, or iBooks Store.
Step 3 Tap something to buy. You'll see a Touch ID prompt.
Step 4 Lightly touch the Home button to make a purchase.
Use Touch ID for Apple Pay
With an iPhone 6 or iPhone 6 Plus or later, you can use Touch ID to make Apple Pay purchases in stores and within apps.