After you register an account on the Guide & File site, you will get an email at the email address you used to register. The email contains an activation link. You do NOT have to click on the activation link to use the Guide & File site.
But you DO have to click the activation link if you want to log in to your state's eFile site. (Click here to find your state's eFile site.) Even if you e-file from the Guide & File site, you may need to log in to your state's eFile site to check the status of your filings or use other features.