Q:

React-Native - Rendering Component on Button click using JSON data

I am completely new to React Native.  So please apologize me for very naive questions. 
I have a main screen which has a button.  When the button is pressed I want to fetch data thru another component and display on the screen. 
I have App.js 
import React from 'react';
import { Button, View, Text } from 'react-native';
import { createAppContainer, createStackNavigator } from 'react-navigation'; // Version can be specified in package.json

import {getMovies} from "./fetchmenu.js";

class HomeScreen extends React. Component {
  render() {
    return (
      <View style={{ flex: 1, alignItems: 'center', justifyContent: 'center' }}>
        <Text>Home Screen</Text>
          <View style={{ flex: 1, flexDirection: 'row', alignItems: 'center', justifyContent: 'center' }}>
            <Button
              title="Menu"
                onPress={() => {
                    <getMovies />   // I want to display data as a result of button press
                  }}
            />
          </View>
      </View>
    );
  }
}

const AppContainer = createAppContainer(RootStack);

export default class App extends React. Component {
  render() {
    return <AppContainer />;
  }
}

And fetchmenu.js
import React from 'react';
import { FlatList, ActivityIndicator, Text, View  } from 'react-native';

export default class getMovies extends React. Component {

  constructor(props){
    super(props);
    this.state ={ isLoading: true}
  }

  componentDidMount(){
    return fetch('https://facebook.github.io/react-native/movies.json')
      .then((response) => response.json())
      .then((responseJson) => {

        this.setState({
          isLoading: false,
          dataSource: responseJson.movies,
        }, function(){

        });

      })
      .catch((error) =>{
        console.error(error);
      });
  }

  render(){

    if(this.state.isLoading){
      return(
        <View style={{flex: 1, padding: 20}}>
          <ActivityIndicator/>
        </View>
      )
    }

    return(
          <View style={{flex: 1, paddingTop:20}}>
            <FlatList
              data={this.state.dataSource}
              renderItem={({item}) => <Text>{item.title}, {item.releaseYear}</Text>}
              keyExtractor={({id}, index) => id}
            />
          </View>
    );
  }
}

How do I display the FlatList created by getMovies on HomeScreen 
when the button is pressed? 

A:

In your HomeScreen set your state like this:
state={showMovies:false}

Then on Button click setState to {showMovies:true}.  And in your render function in App.js:
render() {
return (
  <View style={{ flex: 1, alignItems: 'center', justifyContent: 'center' }}>
    <Text>Home Screen</Text>
      <View style={{ flex: 1, flexDirection: 'row', alignItems: 'center', justifyContent: 'center' }}>
        <Button
          title="Menu"
            onPress={() => {
                this.setState({showMovies:true});
              }}
        />
        {this.state.showMovies&&<GetMovies/>}
      </View>
  </View>
);
}

Since you are exporting getMovies class as default export (not named) do the same with importing:

WRONG: import {getMovies} from "./fetchmenu.js";
CORRECT: import GetMovies from "./fetchmenu.js";

I strongly recommend you to watch some tutorials before getting into real projects. 
EDIT
As @Milore stated Component names in React must start with capital letter.  See this for further information

