Expo/Firestore Compatibility

I'm running a project on expo, but i'm having difficulties implementing the firestore backend into the code. Not that much helpful documentation out there to help with the syntax.

I've created a separate file named usersApi:

import firebase from "firebase"
require("firebase/firestore");
import React, { Component } from 'react';


const firebaseConfig = {
  apiKey: "...",
   authDomain: "...",
   databaseURL: "...",
   projectId: "...",
   storageBucket: "...",
   messagingSenderId: "...",
   appId: "..."
};
!firebase.apps.length ? firebase.initializeApp(firebaseConfig) : firebase.app();


export function addUsers(child, addComplete){

  firebase.firestore().collection('users').add({
    fname: child.name,
    lname: child.name,
    createdAt: firebase.firestore.FieldValue.serverTimestamp()
  }).then((data) => addComplete(data))
.catch((error) => console.log(error));
}
export function getNames(namesRetrieved){

My desired goal is to retrieve the names the user enters into the app on a form sheet and store it in the firestore database. This is in the attendance.js file:

export default class Attendance extends Component {

  state = {
      childFistName: '',
      childLastName: '',
      tableHead: ['First Name', 'Last Name', 'Time in', 'Time out'],
       students: []
    }