The page which you see is our default index.html which is automatically added when you create or add a domain/subdomain from the Domain Manager.
To stop seeing this page you will have to upload your own index page inside your domain/subdomain directory.
You can upload your index file and the rest of your files via the File Manager or FTP client such as FileZilla. Before uploading your index file you might want to delete our default one in case the FTP client fails to overwrite the file.