1. Head over to the Firebase Console.
2. Click "Add project" and just follow the steps to create a new Firebase project.
3. After your project is ready, add an Android or iOS app by following the given instructions.

1. Open up the pubspec.yaml file in your Flutter project.
2. Add these dependencies for Firebase Analytics:
   ```yaml
   dependencies:
   firebase_core: latest_version
   firebase_analytics: latest_version
   ```
3. Run flutter pub get to install the packages.

For Android:

1. Download the google-services.json file from the Firebase Console and drop it in the android/app directory.
2. Open android/build.gradle and add:
   ```gradle
   dependencies {
   classpath 'com.google.gms:google-services:4.3.5' // Check for the latest version
   }
   ```
3. Then, open android/app/build.gradle and add:
   ```gradle
   apply plugin: 'com.google.gms.google-services'
   ```

For iOS:

1. Download the GoogleService-Info.plist file from the Firebase Console and place it in the ios/Runner directory.

2. Open ios/Runner/Info.plist and add:
   ```xml
   CFBundleURLTypes

   CFBundleTypeRole Editor CFBundleURLSchemes YOUR_REVERSED_CLIENT\_ID \`\`\`

3. Make sure to enable the Firebase SDK in the ios/Runner/AppDelegate.swift:
   ```swift
   import Firebase

   @UIApplicationMain
   @objc class AppDelegate: FlutterAppDelegate {
   override func application(
   _ application: UIApplication,
   didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
   ) -> Bool {
   FirebaseApp.configure()
   return super.application(application, didFinishLaunchingWithOptions: launchOptions)
   }
   }
   ```

1. Open the main.dart file.
2. Import the necessary Firebase packages:
   ```dart
   import 'package:firebase_core/firebase_core.dart';
   import 'package:firebase_analytics/firebase_analytics.dart';
   import 'package:firebase_analytics/observer.dart';
   ```
3. Initialize Firebase in the main function:
   ```dart
   void main() async {
   WidgetsFlutterBinding.ensureInitialized();
   await Firebase.initializeApp();
   runApp(MyApp());
   }
   ```

1. Create a Firebase Analytics instance in the MyApp class:
   ```dart
   class MyApp extends StatelessWidget {
   static FirebaseAnalytics analytics = FirebaseAnalytics();
   static FirebaseAnalyticsObserver observer = FirebaseAnalyticsObserver(analytics: analytics);

   @override
   Widget build(BuildContext context) {
   return MaterialApp(
   navigatorObservers: [observer],
   // other properties
   );
   }
   }
   ```

2. Log custom events to track user behavior:
   ```dart
   void _sendAnalyticsEvent() {
   analytics.logEvent(
   name: 'test_event',
   parameters: <String, dynamic>{
   'string': 'string',
   'int': 123,
   'long': 12345678910,
   'double': 123.45,
   'bool': true,
   },
   );
   }
   ```

3. Call _sendAnalyticsEvent method at appropriate places in the app to log events:

```dart
RaisedButton(
onPressed: _sendAnalyticsEvent,
child: Text('Send Test Event'),
);
```

1. Open the Firebase Console.
2. Navigate to the "Analytics" dashboard under the project.
3. View user behavior data, custom events, and other metrics tracked in the app.