The Movies app is a demonstration of basic concepts, such as fetching data, rendering a list of data including images, and navigating between different screens.
You'll need to have all the [prerequisites](https://github.com/facebook/react-native/tree/master/ReactAndroid#prerequisites) (SDK, NDK) for Building React Native installed.
Start an Android emulator ([Genymotion](https://www.genymotion.com) is recommended).
Building the app on both iOS and Android means building the React Native framework from source. This way you're running the latest native and JS code the way you see it in your clone of the github repo.
This is different from apps created using `react-native init` which have a dependency on a specific version of React Native JS and native code, declared in a `package.json` file (and `build.gradle` for Android apps).