The best app lock for android is a third-party app which is Hider. Now follow these steps to install and activate this app:-
1. The first step is to search App Hider on Google Play Store and download it.
2. Then install the app as per the instructions.
3. Now sign up and activate the App Lock.
4. Then perform the instructed steps and set a password.
5. Now finally select certain apps and put it in the app lock.