How to use firebase login with expo

I was following the instructions on Expo's docs, however I was not sure what goes where. I installed firebase using npm. Then the next step is to copy my firebase setup info, which I did from the firebase console.

import * as firebase from 'firebase';

// Initialize Firebase
const firebaseConfig = {
  apiKey: "<YOUR-API-KEY>",
  authDomain: "<YOUR-AUTH-DOMAIN>",
  databaseURL: "<YOUR-DATABASE-URL>",
  storageBucket: "<YOUR-STORAGE-BUCKET>"
};

firebase.initializeApp(firebaseConfig);

But where does this peace of the code go? In root navigation or router? How do I then refer to it in other parts of my app. As you can tell, I'm fairly new to Expo and React-Native, so your help is appreciated.