You can follow the documentation step by step here: https://docs.mendix.com/howto/mobile/deploying-native-app
It tells you exactly what you need to do to obtain a .apk-file for an Android device.
Hope this helps.
I’ve followed the given doc, But after clicking build its showing the following error
I solved the above mentioned issue but, now even though my app opens on the device it is just stuck at the starting splash screen with the mendix logo on it. can you please help me on this one?