Hello and welcome @Brett_Peters 
We have some great guides in Developer Guides that might be worth with having a browse of.
I think a lot of people start with these:
- Beginner's guide to using Discourse Themes
- Beginner's guide to developing Discourse Themes
- Get started with Theme Creator and the Theme CLI
- Designer's Guide to getting started with themes in Discourse
- Installing a theme or theme component
Or if you’re looking for more backend things there’s some plugin guides in there as well.