I can't remember my username or password
You'll only have a username and password if you're a paying member, or have been a paying member before.
Your username is the email address you registered with when you joined. If you've forgotten your password, you can reset it on the same page where you enter your login details.
If you've not received the password reset email after 12 hours, please check your spam / junk folder to check that it's not been filtered out by your email software.
Finally, if you're sure that you're using the correct login details, it may be worth clearing your cache as your device or PC could be struggling with filtering out old information if there have been updates to the site etc. You can find out more about how to do that here.