Go to “Security” under the main menu, then scroll to “2-Factor Authentication”. Press “Enable 2fa”, it will display a QR code. Scan this code with your authenticator app (eg. Google Authenticator) on your mobile. Then enter and confirm the code.

Recommended for Android:

https://play.google.com/store/apps/details?id=com.google.android.apps.authenticator2

Recommended for iOS:

https://apps.apple.com/us/app/google-authenticator/id388497605