From within your Gmail or Google Drive click on your photo in the top right corner and then click "Manage your Google Account"


Click on the Security tab



In the Signing into Google section click 2-Step Verification



Click Get Started



Enter your password and click Next



If you have a linked smart phone you can set this up 



Then you will need to set up a back up option


A good back up option is Google Authenticator 



After setting up your back up option you will be asked to Turn On 2-Step Verification.