You want to add pod 'GoogleSignIn', '~> 4.2' similar to the following to your Podfile:

target 'MyApp' do
  pod 'GoogleSignIn', '~> 4.2'
end

Then run a pod install inside your terminal, or from CocoaPods.app.

Alternatively to give it a test run, run the command:

pod try GoogleSignIn

The CocoaPods Website has an optional integration with AppSight.io that checks every pod you look at for apps which consume it.

AppSight.io is a third-party service which tracks SDKs usage in the top iOS + Android apps.

You can turn it off by clicking here: Disable