This requires the user to enter the Passcode before the user can reach the iPhone's content. Without the Passcode, no one can reach private data on the phone.
Let's say I accidentally put my iPhone down at work and one of my coworkers wants to prank me by messing up settings or changing the name Siri calls me which can embarrass me. The lock keeps that prankster from getting the best of me. Obviously, it also keeps bad guys from getting my banking information or passwords stored in apps like Lastpass password manager.
Watch this following short YouTube video for the step by step guide!