What is the difference between the CSS web portal and the webmail system?

The web portal is this website. It allows you to keep your contact information up to date, see course assignments, quickly contact teachers, parents, etc.

The webmail system is a separate application that is hosted for CSS by Google. We chose to use this email system to reduce our administrative overhead and still offer a truly cutting-edge email, calendar, and document-sharing experience.

What is the relationship between the two programs?