There is also a HowTo in the documentation:
https://docs.mendix.com/howto/custom-widget-development/
Hi, have you seen this learning path?
https://gettingstarted.mendixcloud.com/link/path/45
Maybe it will solve some questions.
Here are two other helpful links to help you get started.
https://docs.mendix.com/howto6/getting-started-with-the-widget-development-plugin-for-adobe-brackets