I entered my email address...it filled in a user name for me.
I then got a confirmation email with a link to set the password.
I clicked on that, set the password, and after that, was able to login.
The personalized link probably expires before 72 hours if the password is set successfully.
Since I had no issues, that seems like how it works.
If you're not getting a confirmation email, check your spam folder in your email client.
If you can't use the registration page, disable any add-ons or use another browser.