Step 1: Open your project directory in Terminal.

Step 2: Run this command to get a podfile started:

pod init

Step 3: Open the Podfile that just popped up in the root of your project with your favorite text editor.

Step 4: Add the Firebase pods to your Podfile like this:

# Uncomment the next line to define a global platform for your project
# platform :ios, '9.0'

target 'YourProjectName' do
  # Comment the next line if you don't want to use dynamic frameworks
  use_frameworks!
  
  # Pods for YourProjectName
  pod 'Firebase/Core'
  pod 'Firebase/Analytics' # Optional, only if using analytics
end

Step 5: Save the Podfile and then run this command to install the pods:

pod install

This will create an .xcworkspace file. From now on, make sure to open your project using the .xcworkspace.

Step 1: Head over to the Firebase Console.

Step 2: Click on "Add Project" and follow the instructions to set up a new project.

Step 3: Choose your iOS app and click on "Add App".

Step 4: Register your app with the correct Bundle Identifier.

Step 5: Download the GoogleService-Info.plist file and add it to your project. Make sure it's included in all necessary targets.

Step 6: Open AppDelegate.swift and import the Firebase module:

import Firebase

Step 7: Configure Firebase in the application(_:didFinishLaunchingWithOptions:) method:

func application(_ application: UIApplication, 
    didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
    FirebaseApp.configure()
    return true
}

Step 1: Pick the Firebase products you want to use (like Firestore, Auth) in the Firebase console.

Step 2: Make sure the corresponding pods are added to your Podfile. For example, to add Firestore and Auth:

pod 'Firebase/Firestore'
pod 'Firebase/Auth'

Step 3: Run pod install again to get these pods installed.

Step 4: Import the modules as needed in your Swift files:

import FirebaseFirestore
import FirebaseAuth

Step 1: Write a simple test to make sure Firebase is working. For example, to test Firestore:

import Firebase

func testFirestore() {
    let db = Firestore.firestore()
    db.collection("testCollection").addDocument(data: [
        "name": "testUser",
        "email": "[email protected]"
    ]) { err in
        if let err = err {
            print("Error adding document: \(err)")
        } else {
            print("Document added successfully")
        }
    }
}

Step 2: Call testFirestore() from your view controller or AppDelegate and run the app.

This step-by-step guide shows you how to integrate Firebase with an existing Swift iOS project.