To retrieve your password, submit your email (assuming you submitted your email as your username). Do not forget to check the google captcha box (to fight spam bots!)
You will receive an email with your password. You can change your password after you log into your account.
Be sure to check your SPAM folder, because that is where the automated email with your password is surely going to end up!
If you did not submit your email as username when creating your account, you cannot get your password back using the automated password retrieval. In that case you should contact the developers (see the menu on your left).