What is app bundle? How can I use it?
from the release notes for n187:
Add ability to build App Bundles (alternative way to create apps for sending to the Google Play Store)
Note: App Bundles (AAB files) can only be used to upload a packaged app to the Google Play Store and cannot be loaded directly into a device or emulator. This is now the required way to upload a new App to Google Play.
Google play store does not accept .apk anymore?