To sign in to Final Draft 13, enter the email address and password that you created at the time of purchase. The regular retail software package still comes with 2 seats (to be used on computers that you own and operate), and you may sign out of Final Draft on one computer and then immediately sign in on another computer. See this article for details.
If you forgot your password, simply click the Forgot Password? link in the sign-in window and you'll be sent an email for a password reset.
Please note that Final Draft staff do not have your password and can't reset it for you. You do have to use the Forgot Password function in the sign-window.