The question is: what are you interested in?
There are some codebases (for example ecto, phoenix) where it will be extremely hard to understand what is going on as a beginner (or even as someone more experienced 
) as they are heavily using metaprogramming.
If you are interested in web, you can take a look at one of my projects that we never managed to finish: SSL MOON / SSL MOON · GitLab . It was developed by beginners, so the concepts there should be pretty easy to understand as long as you read how core technologies like ecto, phoneix, liveview work.
