Initially intended to extend G Suite apps, I like to think of Google Apps Script as a gateway to more kinds of development. Think of it as workflow glue and the power of programming that can interract with Google Apps and external APIs too!
Provide a living document for whenever someone asks, " so, how do i get started with Google Apps Script?".
Just the orgainizing principles and some key links.
Scripts are 'bound' to a container like sheets, docs, slides or forms. These can be accessed from the containing doc and opened say in sheets by going to the menu Tools > Script editor. Scripts can also be standalone for addons or web apps. Your script home page is a dashboard found here script.google.com. The help link there will get you to an explanation of the dashboard.