If you used this website last year you should be able to sign in with the same account details this year. If you can't remember your password choose 'Forgot password' to reset your password. If you have changed your email address since last year you will need to make a new account.
If you have already got an account you can't use the same email address to create a new one - but you probably won't need to. Just choose 'Forgot password' to reset your password and you will be able to reaccess your old account with the same email address as before.