With Apps Script we can power our favorite Google Applications -- such as Gmail, Docs, Sheets, Maps, Calendar, Drive and more.
Apps Script lets us do more with standard Google Apps, which is all powered by Javascript. We can create and customize functionalities into our Application.
Learn more -> here
This is an Apps Sript tutorial
You can find a lot of source codes here with .md explaining the code and what's going on.
This will help with getting started and becoming a better Apps Script developer.