Here's how you can turn on Airplane Mode to prolong your iPhone's battery life.
1. Swipe up fron the bottom to open the Control Center.
2. Tap the airplane icon.
Or you can do it a different way:
1. Go to Settings.
2. Tap on the Airplane Mode button to turn it on.
Airplane Mode can be quite useful if you aren't going to be using cellular or Wi-Fi connections on your iPhone. Why drain the battery down if you don't need to?
Additional resources for iOS