First thing's first, to enable two factor authentication (2FA) you need to be an admin user on your account.
As admin, you can navigate to the follow area:
Now you'll see the option to enable or disable 2FA for all users on the account.
Simply choose to enable or disable and then save the changes.
Once enabled, all users will be required to use a verification code as well as their password to access the account.
By default, the verification code will be emailed however every user has the option to switch to using an Authenticator app such as Google Authenticator, Authy and others.
How to swap to using Authenticator Apps
For users that wish to switch to Authentication via apps, this can be done by going to your user profile (click your name at the top right of embed):
Then select the 'Update two factor authentication' option:
Select the 'Set up authenticator' button:
Then, using your chosen Authenticator app either scan the QR code or enter the setup key and then enter the verification code presented by the Authenticator app to verify the setup. You can then press 'Finish' to complete.