This process will run you through installing and configuring Google Authenticator for Google 2-Step Authenication on Apple and Android devices:

iPhone-

Download Authenticator on the Apple App Store: 

Set up Authenticator
   1. On your iPhone or iPad, go to your Google Account.

   2. At the top, tap Security.
      ○ If at first you don’t get the Security tab, swipe through all tabs until you find it.
      ○ On some devices, Security is located in the side menu.

   3. Under "You can add more sign-in options," tap Authenticator.
      ○ You may need to sign in.

   4. Tap Set up authenticator.
       Follow the on-screen steps.

Connecting Google Authenicator to your Google Account:

On your Computer Go to https://myaccount.google.com

Click on Security on the left side.

Under "How you sign in to Google", choose Authenticator:

The following screen will be presented:

Open the Google Authenticator App on your Phone.

Tap on the Icon at the bottom Right:

Scan the QR code that was displayed on your computer after you Clicked ->

"Set up Authenticator"