GI1 Hi there! As others have said, GrapheneOS includes the "Apps" app which includes the apps that GrapheneOS makes (Auditor, Camera, PDF Viewer etc.) as well as Google Services Framework, Google Play Services and Google Play Store if you want to use Sandboxed Google Play:
Beyond that, you can download any app store you want. GrapheneOS doesn't force you to use a specific one by packaging it with the OS only for you to want to use something else. It's up to you!
If you have any more questions, let us know. Welcome aboard :)