1. Go to the Firebase Console: Firebase Console.
2. Create a Project: Click on "Create a project", follow the instructions, and enter the necessary details.
3. Add Firebase to Your App:
   • For iOS, follow the instructions to register your app with Firebase and download the GoogleService-Info.plist file.
   • For Android, follow the instructions to register your app with Firebase and download the google-services.json file.
4. Add SDK to Your App:
   • For Web, include Firebase SDK scripts in your HTML.
   • For iOS, add the Firebase SDK to your Podfile.
   • For Android, include Firebase SDK in your build.gradle files.

1. Navigate to Authentication: In the Firebase Console, go to the "Authentication" section.
2. Click on Sign-in Method: Locate and click on the "Sign-in method" tab.
3. Enable Anonymous Sign-in:
   • Find the "Anonymous" provider.
   • Click on the "Enable" toggle.
   • Save the changes.

For Web:

1. Initialize Firebase:

   ```javascript
   // Import Firebase
   import { initializeApp } from "firebase/app";
   import { getAuth, signInAnonymously } from "firebase/auth";

   // Firebase configuration
   const firebaseConfig = {
   apiKey: "YOUR_API_KEY",
   authDomain: "YOUR_AUTH_DOMAIN",
   projectId: "YOUR_PROJECT_ID",
   storageBucket: "YOUR_STORAGE_BUCKET",
   messagingSenderId: "YOUR_MESSAGING_SENDER_ID",
   appId: "YOUR_APP_ID"
   };

   // Initialize Firebase
   const app = initializeApp(firebaseConfig);
   const auth = getAuth(app);
   ```

2. Sign in Anonymously:

   ```javascript
   signInAnonymously(auth)
   .then(() => {
   console.log("Signed in anonymously");
   })
   .catch((error) => {
   const errorCode = error.code;
   const errorMessage = error.message;
   console.error("Error: ", errorCode, errorMessage);
   });
   ```

For iOS (Swift):

1. Import Firebase:

   ```swift
   import Firebase
   ```

2. Configure Firebase in AppDelegate:

   ```swift
   @UIApplicationMain
   class AppDelegate: UIResponder, UIApplicationDelegate {
   var window: UIWindow?
   
   func application(_ application: UIApplication,
   didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
   FirebaseApp.configure()
   return true
   }
   }
   ```

3. Sign in Anonymously:

```swift
Auth.auth().signInAnonymously() { (authResult, error) in
if let error = error {
let errorCode = (error as NSError).code
let errorMessage = error.localizedDescription
print("Error: (errorCode) (errorMessage)")
} else {
print("Signed in anonymously")
}
}
```

For Android:

1. Add Firebase Auth Dependency:

   ```gradle
   dependencies {
   implementation 'com.google.firebase:firebase-auth:21.0.1'
   }
   ```

2. Initialize Firebase in Application class or main Activity:

   ```java
   import com.google.firebase.auth.FirebaseAuth;

   // Initialize Firebase Auth
   FirebaseAuth auth = FirebaseAuth.getInstance();
   ```

3. Sign in Anonymously:

```java
auth.signInAnonymously()
.addOnCompleteListener(this, task -> {
if (task.isSuccessful()) {
// Sign in success
Log.d("FirebaseAuth", "signInAnonymously:success");
} else {
// If sign-in fails, display a message to the user.
Log.w("FirebaseAuth", "signInAnonymously:failure", task.getException());
}
});
```