Parents can access the system by clicking any of the links in the emails they receive, or by logging on directly using their email address and password at the domain you will have been given, typically https://yourschoolname.schoolpost.co.uk.
They can set/reset the password to something of their own choice by following the ‘request password reset’ link on the login page and following the instructions from there. There are also options to authenticate parents against other systems such as Firefly and common parent portals.
Changing your settings
Main Menu > My Settings > Email notifications