To start or use a session you must use session_start(); right at the top of your script.
Eg,
<?php
session_start();
?>
You can then store any number of variables in the session superglobal, like so....
<?php
session_start()
$_SESSION[state]="Timbuck Two";
$_SESSION[month]="December";
print "The variables have been registered";
?>
To recall them...
<?php
session_start()
print "The State was ".$_SESSION[state];
print "The month was ".".$_SESSION[month];
?>