Sometimes you may need to show people stuffs on your phone or give them to fix for you, then the next thing you see is that they are nosing through your phone? This can be very annoying especially if this is done by somebody you respect so much or maybe you want to give your phone to kids but u are always worried but them activation or deactivation of settings. Maybe you are a guy that don’t like your girl to route through every nook and cranny of your phone.

Method 1

Then Screen pinning is exactly what you need
Screen pinning enables you to make the current application to stay on screen actively without allowing the user to exit or minimize it without unlocking the phone. They can only use the pinned app and not access other part of the phone
To Set up Screen Pinning:
1. From the top of the screen, swipe down to reveal the notifications bar.
2. Tap the date & time area of the notification bar, then tap the gear icon to open the Settings screen.(or just open settings on your menu)
3. From the "Settings" screen tap "Security" > "Advanced" > "Screen Pinning" > and then set the switch to the "ON" position.
4. Open the application you want to pin
5. Tap the overview button i.e the button you use to minimize or view minimized apps
6. Swipe up and then tap the pin icon

The instructions for how to use screen pinning are located directly under the setting itself.



Method 2

Guest Mode

The guest mode feature allows you create a user profile that your children (or anyone that will use your phone for a while) can use. This profile is separated from your personal profile so no one can see or mess with your data, pictures, videos, not even your apps. This allow them to install apps from the Google Playstore and if the app is already on your phone, it will be copied to the guest profile (instead of having to download it again).
In addition to the Guest profile, you can actually create personal profile for people just as in pc. With each person right to customized their profiles.
Note: These features require that your device has Android 5.0 (or later) OS installed.

To Set up Guest Mode:

1. From the top of the screen, swipe down to reveal the notifications bar.
2. Double-tap your profile image from the top-right corner.

Three icons will appear, your Google account, "Add guest" and "Add user".
3. Select the "Add guest" option.
4. Once you've selected the "Add guest" option, your device will probably take a couple of minutes to complete the Guest Mode setup process.
When your finished with guest mode you can switch back to your profile by repeating the first two steps above.

source

http://www.emperorconcept.com/2017/11/how-to-restrict-people-to-only-one-app_55.html