How should I go about putting together a server-side scripted website
that uses session cookies and user authentication?

[My current skills: 
I am good with Java, C++, and basic PHP scripting.

What I want to do: 
Make a website that asks questions over a series of web-pages and then
gives advice based upon the answers. I want user-authentication so
that people can revist the site later and start where they
left-off...]