At the highest level, Google Apps Script (GScript for short), is a scripting platform for light-weight development across the entire Google Suite ecosystem. Each GSuite “app” (Sheets, Docs, Calendar, etc…) is referred to as a GScript service. Each service, such as the Google Sheets service we’ll strictly focus on throughout this article, is made up of multiple classes — each with the typical class structure of properties & methods.
You’re likely using Google Sheets already, so why not take a few minutes to learn how to customize & automate it to your particular needs? With Google Script, Google has made it extremely easy for anyone to extend Sheets.
Source: Starting With Google Script