DOOM's look is loosely inspired by Atom's One Dark theme, and is largely contained in the [[https://github.com/hlissner/emacs-doom-theme/][doom-themes]] plugin.
If you're getting strange unicode symbols, that is likely ~all-the-icons~ doing (caused by other UI modules, specifically [[../doom-modeline][doom-modeline]] and [[../doom-dashboard][doom-dashboard]]).
You must install the fonts included with ~all-the-icons~ with: ~M-x all-the-icons-install-fonts~.