The site automatically generates a password when you register.
You need to either save the password, write it down and keep it.
You can change your password to one which is easier to remember by clicking on log in and then click on the reset password or forgot password link. You will need to enter either the email address with which you registered or your username.
You will receive an email with a link to reset your password. Once you click on the link and go to the reset password page, you will be able to change your password to whatever you want.
Of course if you have any trouble, simply email me and I can do it for you.