A few users are familiar with Google Apps Script (or GAS) to implement features such as data import, emails, SMS, charting etc. and you will find some posts here relating to that.
I just came across a learning resource called Google Apps Script: Access Google Sheets, Maps & Gmail in 4 Lines of Code which is hosted at Qwiklabs. There are many other free and paid labs/courses there to learn lots of cool stuff. I am not sure if it would be possible to put AppSheet training stuff there as well but it would be cool to have it there.
Disclaimer: I have no affiliation with Qwiklabs and am not advertising for them. Just sharing since people are looking to learn more about how to leverage not only AppSheet but cloud technology in general.