This is the project for Ben Collins' Intro to Apps Script course, which is an amazing free course that I would recommend for any beginner that's looking to do spreadsheet development. His lectures are relatively short and he explains the material quite well.
I've also used the repository he made for the course as reference material, which can be found here.
From my personal experience, he emphasizes that you should follow along with his lectures by having spreadsheets of your own, which I've found to be helpful. There are spreadsheet templates linked in the modules, so you don't have to worry about making your own.