build.gradle(Module:app) file when you need to add new libraries to your project or change library versions.app and res folders. The java folder includes activities, tests, and other components in Java source code. The res folder holds resources, such as layouts, strings, and images.AndroidManifest.xml file to add features components and permissions to your Android app. All components for an app, such as multiple activities, must be declared in this XML file.Log statements to your app, which display messages in the Logcat pane as a basic tool for debugging.