Much like hell, OneShot modding is split into layers, where the deeper you go, the more suffering you must endure:
Each layer describes what it covers, and a set of requirements, so be sure to read through them all to decide which layers you’ll be working on.
While you may be working on multiple layers at once, they’re independent of each other for the most part. For example, you can modify scripts without touching the assets, or vice versa.
And while not required for most layers, having the editor allows testing your changes easily.