To get your user agent just copy and paste the value from http://www.useragentstring.com/ into the user agent box.
To get the cf_clearnance value: Go to http://www.gametracker.com/search/bf3/, next to the address bar in Chrome on the left hand side, click the page icon. You should see this:-
From click on the link. From there click on the link to see your cookies:-
After that you need to expand each section until you can see each cookie. If no cf_clearance cookie is present, that means CloudFlare is not active and you can paste anything in the text box on PBSS Scanner. If the cookie is there copy the content/value of the cookie into the text box.