App:

It DESCRIBES the basic characteristics of the application and defines each of its components.

java:

• This contains the .java source files and .kt(source code written in Kotlin) source files of your project. By default, it includes a MainActivity.java or MainActivity.kt source file.
• You create all the activities which have .java and .kt extensions under this file and also it includes all the code behind the application.

res:

• It is used to store the values for the RESOURCES that are used in VARIOUS Android projects to include features of color, styles, dimensions, etc.
• It is a directory for files LIKE styles.xml, strings.xml, colors.xml, dimens.xml, etc.

Scripts:

This is an auto-generated file that consists of compileSdkVersion, buildToolsVersion, minSdkVersion, targetSdkVersion, applicationId, versionCode, and versionName. For example, build.gradle is a script file placed in the root project directory, defines build configurations that will be APPLIED to all modules in your project.