Here are some good tutorials I have found that teach sessions in PHP.

A session is like a cookie that is stored on the site's web server instead of the users computer. This makes them more secure than a cookie because the user has NO access to it and therefore can not hack into it and change something.

Sessions therefore play a BIG role in dynamic sites!

zend.com
codewalkers.com
free2code.net
tizag.com
tutorialized.com
http://www.brainbell.com/tutorials/php/ ... d_Sessions).htm
plebian.com

Later

Session can handle the user info and required information that we want to have thruoghout our visit to desired website.

Session support in PHP consists of a way to preserve certain data across subsequent accesses. This enables you to build more customized applications and increase the appeal of your web site.
to read more visit PHP SESSION