Basically, sessions let you store key/value pairs that can be used between pages without having to pass the data in a URL or with a form. There are two main methods of doing this; either through cookies or through a URL. You can choose either, based on your setup.
You need to tell each page that will be accessing the session data, to start using the session when it loads. Read about the session_start() function.
Once you start a session, you need to register some variables, that is to say, make them available to the session for use on other pages. This is done with the session_register() function.
You may remove one or more of your session variables with the session_unregister() function. This will keep the session intact, but will remove a specified value.
To kill a session, use the session_destroy() function.
In your situation, I would start a session on the first signup page, register any variables that will be used throughout all your pages. Add the session_start() function to the top of all pages that need access to the session variables and then access each variable where necessary.
