Your question needs clarifying.
Google created the base operating system of Android.
The phone makers build launchers and services and apps at the medium and high levels of the computing system.
Google's part here is required.
Google also makes high-level apps for the Android phones. All of the Google apps are optional except for the Play Store app. While they are optional, meaning you don't have to use them, many of them are automatically installed on your phone as part of the licensing agreement with the phone makers.