下面以依赖english_words包为例
1.pubspec 文件为Flutter app 管理资产和依赖，所以首先要在pubspec.yaml中添加 english_words (3.1.0 or higher) ：

dependencies:
  flutter:
    sdk: flutter
  cupertino_icons: ^0.1.2
  english_words: ^3.1.0

2.执行Package get，把包下载到当前项目。

$ flutter packages get
Running "flutter packages get" in startup_namer...
Process finished with exit code 0

此时会自动在pubspec.lock文件中列出已经下载到本项目的包和他们的版本等信息。
3.在lib/main.dart中导入包：

import 'package:english_words/english_words.dart';

4.在main.dart中使用它：

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final wordPair = WordPair.random();
    return MaterialApp(
      title: 'Welcome to Flutter',
      home: Scaffold(
        title: Text('Welcome to Flutter'),
      ),
      body: Center(
        child: Text(wordPair.asPascalCase),
      ),
    )
  }
}

5.选择设备,运行。

flutter device
flutter run