Hi Panagiotis - this post originally was describing our old visual builder. Now we are using new approach for creating backend with your apps, please learn more here: https://docs.appery.io/docs/apiintegr...
As for Sever Code you can use it in today's version too, here you can find more details:
:: https://docs.appery.io/docs/servercod...
:: https://docs.appery.io/docs/quickstar...