press Control Alt F5 (Or any F key other then F1 and F9) at the same time. this will put you in a log in terminal.
type root as the username, and the root password as the password. (I doubt the installer is dumb enough not to let you set the rot password, but thats faith in the programmer)
This shoudl give you a long MOTD (Msg Of The Day), and an # prompt. So at the # or what ever the prompt is
It will then ask you a number of questions, anwser them; if you don't understand any the default is prolly ok - if problems from it write down what you anwsered to what and post.
After this is all done, press Control Alt F9 and log in with the user name you created.
You can add more users this way from Konsole, or using the GUI based ultilities provided by PC-BSD. If you need to allow root to log in to use the GUI instead, well we can help there too but it's not the most secure that way.