There are a few different ways that you can download the Google Authenticator app. The first way is to go to the Google Authenticator website and click on the "Download" button. This will take you to the Google Play Store, where you can install the app on your Android device.
Another way to download the app is to search for "Google Authenticator" in the Google Play Store and install the app from there.
Once you have installed the app, you will need to set it up with your Google account. To do this, open the app and tap on the "Begin setup" button. Then, follow the on-screen instructions to add your Google account and set up two-factor authentication.