very simple question indeed.
register to the play store.
finish your app, export it with a signed key, it generates a file.
go to the play store, create new app, put name, decription etc and upload that file.
make changes/improvements/bug fixed to your app, export it with the SAME signed key, it generates another file.
go to the play store, enter the existing app, upload the new file, mark it as active.
