1. Initially, iPhone doesn't require you to enter a passcode to unlock it. You can set a passcode that must be entered each time you turn on or wake up iPhone.
   
2. Set a passcode:
   
   Go to Settings.
   
3. Tap General.
   
4. Scroll to, then tap Passcode Lock.
   
5. Tap Turn Passcode On.
   
6. Set a 4-digit passcode.
   
7. To change a passcode, tap Change Passcode.