All of our React Native codebases are making use of a subset of Core Modules, which the strategy we use to make our code of high-quality and highly modularized. These are submodules that are implementing specific parts of a mobile app, and that are independent and reusable between each other. The all live in src/Core, and can be modified and customized by you as needed. 
As you can see, there’s a decent number of such core modules, such as:
- Onboarding
- Authentication
- Firebase
- Localization
- Location
- Camera
- Chat
- Video Chat
- WooCommerce
- Stripe
- Profile
- etc.
The name of each module should be self-explanatory, so you can dig only into the parts of the app that you are interested in understanding or customizing.