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).
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.