You may need to first enable Screen pinning.

• Launch the Settings app on your Android device.
• Scroll down until you find the Security option. Tap on it.
• At the bottom of the Security page tap on Screen pinning.
• Slide the switch to the On position.

​To pin an app: Tap on the overview button (it's the square button along the bottom of your screen) that shows all your current running apps.

• Drag the title bar for the app you're going to pin up, until it's in the middle of the screen.
• In the bottom-right corner of the app overview will be a blue pin button. Tap on it.
• Each time you pin an app, you'll be asked to confirm the action. You'll also have to decide if you want to require a security code to leave the pinned app.
• Tap on Start to pin the app.

Exiting a pinned app requires you to touch and hold the back and overview buttons at the same time. After a couple of seconds, your device will switch to the overview screen.You can set up other means of exiting pinned apps with the swipe security or pin numbers.