The Android studio is labeled as the official IDE (Integrated Development Environment) for Google Android operating system. Applications are built on this Android Studio by developers, and they have the option to re-edit and do whatever changes they require to perform for the applications that they build using the platform. These applications built could then be compiled into APK format and then be submitted Google Play Store. Once approved you could download these apps from the store.
If you wish to get trained and skilled in Android, then I would suggest you enroll in Intellipaat’s Android course from Intellipaat, which offers you the training course and guided projects to help you become a certified professional. Also, check out our YouTube video on the Android Application Architecture to help you get started.