Follow this guide.

TL;DR:

1. brew install node
2. brew install watchman
3. npm i -g react-native-cli
4. Install Xcode.
5. Install Android Studio according to the guide.

To run:

• react-native run-ios
• react-native run-android

I'm pretty new to react native so I guess I'll follow a file structure like this. index.ios.js and index.android.js are both going to point to app/index.js, so that file will be our unified entry point. Basically, we shouldn't need to edit anything outside of app/.