It's basically a repo containing ~/.emacs.d. It provides a lot of sensible defaults for different Emacs packages, these are organized into "modules" which are

It's basically a repo containing ~/.emacs.d. It provides a lot of sensible defaults for different Emacs packages, these are organized into "modules" which are just sub-folders that can be enabled or disabled via the central config files in ~/.doom.d (this is a custom Doom thing, it just loads a few files in ~/.doom.d at startup to make it easy to config everything in one place). Basically it provides you a nice starting point to using Emacs, with things just working out of the box.