Yubikey is one of the most simple and safe ways to set up 2FA. Further information can be found here.
If you already have an XGo account, you can use it to log into the app. However, if you use a Yubikey as the only means of two-factor authentication, you'll need to add a 2FA app as another method of two-factor authentication on our website before you can sign in to our app. Then just use the one-time code to sign in to your account.
For more information on 2FA, just take a look here.