In prev step we install dependencies, install plugin Citybook Mobile App and run app now we export app to apk file:

1. Android requires that all apps be digitally signed with a certificate before they can be installed, so to distribute your Android application via Google Play store, you’ll need to generate a signed release APK.
   You can generate a private signing key using keytool. On Windows keytool must be run from C:\Program Files\Java\jdkx.x.x_x\bin
   Run $ keytool -genkey -v -keystore my-release-key.keystore -alias my-key-alias -keyalg RSA -keysize 2048 -validity 10000
   It then generates the keystore as a file called my-release-key.keystore
2. Place the my-release-key.keystore file under the android/app directory in your project folder.
   
   Edit the file android/gradle.properties, and add the following (replace ***** with the correct keystore password and key password)
   
3. Open cmd then run cd ‘ link folder mobile app ‘
   eg: cd ‘/Users/dev1/Desktop/Projects_IMPORTANT/Citybook/’
4. With macOS : In folder mobile app run cd android then run ./gradlew assembleRelease
   With Window: In folder mobile app run cd android then run gradlew assembleRelease
   
5. Done now we have apk file in ‘android/app/buid/outputs/apk/release’
   
   
6. More infomation here: Generating Signed APK