See apps you’ve opened. Double-click the Home button when iPhone is unlocked. See Start at home.
Use Siri or Voice Control. Press and hold the Home button. See Make requests and Voice Control.
On iPhone models with Touch ID, you can use the sensor in the Home button to read your fingerprint, instead of using your passcode or Apple ID password to unlock iPhone or make purchases in the iTunes Store, App Store, and iBooks Store. See Touch ID. If you have iPhone 6 or iPhone 6 Plus, you can also use the Touch ID sensor for authentication when using Apple Pay to make a purchase in a store or from within an app. See Touch ID and Apple Pay.
You can also use the Home button to turn accessibility features on or off. See Accessibility Shortcut.