Could not create/generate .apk and .ipa files for Ionic 4 application

Currently I am working with ionic 4 application and I have installed all required things like Nodejs, cordova, Ionic, Git, Android Studio, JDK, Android SDK Tools...etc. The web application is working fine with any browser, But I could not create/generate .apk and .ipa files for the mobile devices for my existing ionic application, Please help me on this.