Recently, Google has released the Android Studio 0.4.0 and this update brings in support for the new Android Gradle plugin 0.7.0, which has various improvements for render script,ProGuard, lint, BuildConfig and various additions around source folders. The Android 0.4.0 is updates with various issues which are solved. Feeling lost as a developer, then check out the Build System Documentation.
NOTE : The Android Studio 0.4.0 requires the the new version of the Gradle plugin. Migrate all your existing projects to 0.7.0.