To create yourself an account you must visit their Facebook page and click on the registration link. Only when you enter the registration site by the Facebook may you register! After that register, download and enjoy.
There is an upcoming stat reset for Heroes of Newerth so this is a great time to get an account as everyone will be on equal footing soon. So go ahead and register, once again the Heroes of Newerth official Facebook page is http://www.facebook.com/heroesofnewerth.