You will automatically be assigned a new password when you sign up, so check your initial welcome email. However, if you've forgotten your account password then you'll need to reset it.
You can do this by clicking the Forgotten Password link on the login screen and then entering your email address and submitting the form. You will receive a reset link by email which will allow you to set a new password.
All passwords are stored using one-way encryption so that they cannot be retrieved by either ourselves or anyone with malicious intent. Each time you log in we run the same encryption process and if the results match then that means it's the same password.