Esri Tutorial covers most part of the content for you to get up and running a customized widget that can be used in the Web Appbuilder.
However, the current release of the Appbuilder (1.3) is still buggy and doesn't cover some on-demand customization. Here are some points that will come in handy when you need them.
- create a
dev-config.json
—> use it in webappviewer. - https://localhost:3344/webappviewer/?config=dev-config.json