This feature can be found in the 'General Settings' of the Apple device within the 'Accessibility' tab. Be sure to have the 'Guided Access' setting enabled.
Before setting the passcode 'Accessibility Shortcut' should be off and 'Display Auto Lock' should be set to 'Never'.
Select 'Passcode Settings' to register a passcode. Once password is set you'll be able to start using the guided access feature.
To ENABLE/DISABLE Guided Access, triple-click the home, side, or power button (newer models) in the app you want to use. Once activated consumers will not be able to navigate the device in anyway.
***BE SURE TO SAVE YOUR PASSWORD TO AVOID BEING LOCKED OUT OF DEVICE***