Alright, first things first, you need to get the Firebase Unity SDK into your Unity game project. Head over to the SDK directory and import the Firebase Messaging package. Simple, right?

Next up, go to the Firebase console. You can either create a new Firebase project or pick one you already have. Add your Unity game to this project by following the console instructions. Once you're done, download the google-services.json or GoogleService-Info.plist file and drop it into your Unity project.

Open your Unity project and navigate to Assets > Firebase > Messaging > Settings. Upload that google-services.json or GoogleService-Info.plist file you just downloaded. Make sure the enabled checkbox is ticked in the Unity project settings.

Now, you need to initialize the Firebase library when your app starts. Create a script and call Firebase.Messaging.FirebaseMessaging in your main scene to get Firebase up and running.

using Firebase;
using Firebase.Messaging;
void Start()
{
  FirebaseApp.DefaultInstance.SetLogLevel(Firebase.LogLevel.Debug);
}

To handle incoming messages, subscribe to the FirebaseMessaging.MessageReceived event. This event will trigger whenever a new message comes in.

FirebaseMessaging.MessageReceived += OnMessageReceived;

Then, create the OnMessageReceived function to process those incoming messages.

public void OnMessageReceived(object sender, Firebase.Messaging.MessageReceivedEventArgs e)
{
  // Handle the message
}

Firebase Cloud Messaging uses tokens to identify devices. To handle these token responses, subscribe to the FirebaseMessaging.TokenReceived event.

FirebaseMessaging.TokenReceived += OnTokenReceived;

And then, implement the OnTokenReceived function to manage the token responses.

public void OnTokenReceived(object sender, Firebase.Messaging.TokenReceivedEventArgs token)
{
  // Handle the token
}

Finally, it's time to send a push notification. You can do this from the Firebase console in your project. Set the title, text, and other parameters of the message, then publish it. Firebase will take care of sending this notification to all the eligible devices.

By following these steps, you should be able to enable Firebase Cloud Messaging in Unity and handle push notifications like a pro. It might seem a bit tricky at first, but once you get the hang of it, it's pretty straightforward. And hey, it can really boost the user experience of your Unity game!