That's where this is stored?
Can be stored on the device (internal memory or SD card), then use SQLite for local, rather embedded database interaction directly through
ORM either, but if you need access from other instances of the application, you will need a server with any database and the usual REST (HTTP) API for hosting on a VPS/VDS as well as with the sites.
Do I understand correctly that one can not do Java when writing an application for Android? Or is it 90% of the say all that is necessary?
Java is just the syntax and nothing more, you need to learn to work with the SDK and libraries such as mentioned
and ORM, and in the case the server will need a library for REST API (HTTP requests), again, is built into Android, and there are third-party high-level, Retrofit, for example, or you can write also a very good UI you need to learn it on mobile devices is very abstract, so is rather complicated.