With 2-Step Verification, also called two-factor authentication, or 2-FA you can add an extra layer of security to your account in case your password is stolen. After you set up 2-Step Verification, you can sign in to your account with:
Enabling 2-Step Verification
Open your Google Account. Or click on your icon in the upper right corner of you Gmail account.
Then Select "Manage Your Google Account"
In the navigation panel, select Security.
Under “Signing in to Google,” select 2-Step Verification 
Get started.
If you have already attached your phone to your Google Account you may already see it. If so click "Continue". If you have not set a Phone to use with Google, select "Show more options"
If you have not chosen a phone number you will be prompted to do so on the next screen. Enter in a phone number, and select if you want to receive a call or text message. Then select "Send" The system will then send you a text message, or call the number you provided and give you a security code which you will need to enter on the following screen.
Enter the code you were provided by Google and click "Next"
Once done, confirm the information on the last page and select "Turn On" - 2-Step Verification will now be enabled for you Google Account.
After you turn on 2-Step Verification, you must complete the verification step to verify it’s you each time you sign in to Google.