It is the same like some of us did it with aion for example. By typing in the ID and PW (in this case, you have NO account), it will proceed as usual, trying to log you into the game and fetching your data through the whole process, but the account managing instance will recognize "oh wait, there is no account like this", it won't spit out the typical "There is no ID or Password with this bla bla bla", instead, it will fetch those new entered information to the database, like you would create a new account via a website.